Embryology
Q.1 When does the blastocyst get implanted in the uterine wall?
The implantation starts at 7½ days and is completed by the 10th day (Fig. 1.1).
Q.2 What is an organizer?
Organizers are those which are concerned with early histogenesis and development.
Q.3 Give an example of a good organizer.
Primitive streak is the best organizer in the early stage.
Q.4 What is twinning?
The birth of two human infants at a time is twinning.
Q.5 What is ectopia cardia?
This is a condition where there is a developmental defect of the sternum and pericardium.
Q.6 What are the types of twinning present?
There are monozygotic and dizygotic twins. The monozygotic or monoovulatory twins are due to the fertilization of a single ovum by a single sperm. They are defined as true or identical twins.
The dizygotic twins are a result of the fertilization of two ova produced during the same ovulatory phase by two sperms. The dizygotic twins unlike monozygotic have different genetic constitution and could be of different sex. They are also called fraternal or unlike twins and are usually dischorial (Figs 1.2 and 1.3).
Q.7 What is superfecundation?
It is the fertilization of two ova produced from the same ovulatory phase by two sperms from two separate sexual encounters.
Q.8 What is superfetation?
It is the fertilization of two ova produced during separate ovulation cycles.
Q.9 What are the arterial arches left over in the humans?
There are three arterial arches which are left over which are 3rd, 4th and 6th arches. The common and the internal carotid arteries are from 3rd arch. The right subclavian is from right fourth arch. The arch of aorta is from the left 4th arch. The pulmonary arteries present on both sides are from 6th arch.
Q.10 Why is the left innominate vein longer than the right innominate vein?
The left innominate vein is longer than the light one because it is formed by the communication between the anterior cardinal veins and the functional part of the left cardinal vein.
Q.11 Why is the left branch of portal vein longer than the right branch?
This is because it is formed by the fusion of the left vitelline vein and anastomoses present between the two vitelline veins.
Q.12 Why does the thoracic duct opens at the junction of internal jugular and subclavian veins?
The thoracic duct begins at the cisterna chyli, passes obliquely from 7th to 5th thoracic vertebra and goes upwards to the left side. During development of the thoracic ducts, there is a communication between the ducts, passing obliquely from the right 7th thoracic to the left 5th thoracic vertebra. The right part of the duct above the communication and the left part below the communication disappear. The thoracic duct finally opens at the junction of internal jugular and subclavian veins.
Q.13 What is supernumerary cusps of the cardiac valves?
This is a defect due to the atypical division of the cusps of the primordia.
Q.14 What is double aorta?
This is due to the non-disappearance of the right dorsal aorta.
Q.15 Why does the diaphragm get its nerve supply from the phrenic nerve?
The diaphragm during development is in the cervical region which is supplied by the cervical 3rd, 4th and 5th segment nerves, which is the phrenic nerve. With the descent of the diaphragm the phrenic nerve also descends and this phenomenon is known as “neurobiotaxis”.
Q.16 Why is the left renal vein longer than the right renal vein?
This is because it is formed by the fusion of the subcardinal anastomotic channel and the primitive left renal vein.
Q.17 Why is the submandibular salivary gland fixed anteriorly, whereas, the posterior part is free?
The submandibular gland is fixed anteriorly as it develops in the floor of the pharynx and the starting point is at the frenulum. The posterior part is free because it is not in the floor of the mouth cavity.
Q.18 What is coloboma of the iris?
It is due to the non-fusion of the fetal fissure, which is the inferomedial part of the eye (Fig. 1.4).
Q.19 What is the reason for the oblique facial cleft?
This is due to the non-fusion of the frontonasal process with the maxillary process.
Q.20 Why are there three lobes in the right lung and two lobes in the left lung?
The lung is an endodermal derivative. The right lung bud gives rise to two monopodial diverticulae, whereas the left bud gives rise to only one monopodial diverticula and hence there are three lobes in the right lung and two lobes in the left lung.
Q.21 Why there is more growth of the dorsal part of the stomach than the ventral part?
The dorsal part is mainly supplied by the dorsal aorta, hence the growth is more on the dorsal aspect of the stomach.
Q.22 What is the cause of sinus in the middle of neck?
The sinus in the midline of the neck may represent the remnant of thyroglossal duct.
Q.23 What is the cause of lateral sinuses in the neck?
It is due to remnant second and third pouch, which are located in front of the sternocleidomastoid muscle.
It is due to intrathoracic herniation of the cardia with a part of the stomach and peritoneal covering over it. It occurs through a weakness in the esophageal opening of the diaphragm (Fig. 1.5).
Q.25 What is cleidocranial dysostosis?
This is a condition, where there is partial failure of ossification of membrane bones and this affects the vault of the skull primarily. This may also lead to the non-fusion of the fontanelles.
Q.26 What is plagiocephaly?
Plagiocephaly is a condition developed due to fusions and asymmetrical conditions.
Q.27 What is cranioschisis?
The membranous bones of the skull fail to ossify giving rise to a wide open vault of the skull which is known as cranioschisis. This is associated with anencephaly, where the brain fails to develop.
Q.28 What is hypertelorism?
This occurs when there is overgrowth of the lesser wing of the sphenoid bone. In this condition, the eyes are separated abnormally and this is seen in Down syndrome.
Q.29 What is amastia?
The absence of one or both breasts is termed as amastia.
Q.30 What is a crater nipple?
The “crater nipple” occurs due to the failure of mesodermal elevation at the epidermis. There is congenital retraction of the nipples and downward growth of the lactiferous duct.
Q.31 What is Meckel's cartilage?
This is the mandibular arch (I arch) cartilage. It is represented in the mandibles as the genital tubercles, anterior part of the coronoid process and a thickened area between the head of the mandible and the lingula.
Q.32 What is microcephaly?
The brain does not develop properly. It is characterized with the presence of a small brain and cranial cavity.
Q.33 What is horseshoe kidney?
This is a condition, where the caudal ends of the metanephros fuse to form a “u” shaped kidney. It is located in front of the abdominal aorta. The ureters are in the normal position (Fig. 1.6).
Q.34 What is ductus venosus?
It is a communication between the left umbilical vein and the right hepatocardiac channel. This becomes ligamentum venosum after birth.
Q.35 How would you differentiate between embryological and pathological Meckel's diverticulum?
The embryological diverticulum has all the layer of the intestine, whereas, the pathological may not have all the layers as it is diseased.
Q.36 How can you differentiate exomphalos and congenital umbilical hernia?
Exomphalos has no umbilical sac. The congenital umbilical hernia may be paraumbilical or may above or below the umbilicus and usually has a sac (Figs 1.7 and 1.8).
Q.37 What is the cause for the development of double ureters?
The ureter develops from the ureteric bud of the mesonephric duct, if it starts to divide before reaching the metanephric cap, it gives rise to double ureters.
Q.38 What is a weeping umbilicus?
It is due to the externalization of the epithelium of the vitellointestinal duct which is red in color.
It is allantoic diverticulum from the yolk sac. This will form a median umbilical ligament in the adult.
Q.40 What are the components of placenta?
Placenta is defined as having two components with the maternal component being decidua basalis and the fetal component being chorion frondosum (Fig. 1.9).
Q.41 What is chorion frondosum?
It is tertiary chorionic villi which are composed of umbilical vessels, extra embryonic mesoderm and trophoblasts (Fig. 1.9).
Q.42 What is a true hermaphrodite?
This occurs when there is an ovary on one side and the testis on the other side. Sometimes both could be either side and this is known as ovotestis. This usually has a genetic predilection with nearly 53–54% having normal chromosomal build up whereas the remainder may have mosaic patterns such as 44 XXY, 44 XX, or 44 XY.
Q.43 What is a pseudohermaphrodite?
This is a condition when a person externally may appear to be a male or female but characterized by the presence of an opposite phenotype.
Q.44 What is Down syndrome?
This is also called “trisomy 21”. It is quite a common condition, where the chromosome number is 47. It is due to meiotic nondisjunction with translocation occurring at the level of the long arm of chromosome 21. The extra chromosome is maternal in origin. The clinical features are mental retardation, cardiac malformations, presence of epicanthic folds, recurrent infections, wide gap between great toe and second toe, small mouth, large tongue.
Q.45 What is Edward's syndrome?
This is trisomy 18, 47X. It commonly affects the females. The clinical features are mental retardation, prominent occiput, overlapping fingers, micrognathia, developmental defects of heart and kidney and presence of rocker-bottom feet.
Fig. 1.9: Formation of chorion frondosum and chorion laeve
Note: Three parts of decidua—1. Decidua basalis, 2. Decidua capsularis and 3. Decidua parietalis
Q.46 What is Patau's syndrome?
This is trisomy 13. The clinical features are microcephaly, mental retardation, microphthalmia, harelip, cleft palate, cardiac abnormalities, polydactyly and short fingers, umbilical hernia and developmental defects of the kidney.
Q.47 What is Klinefelter's syndrome?
This is seen in males characterized with the presence of an extra sex-chromosome. The extra “x” chromosome may be from paternal or maternal side. The clinical features are hypogonadism, elongated body due to increased length between pubis and sole, small penis, azoospermia, sterility, gynecomastia, testis are reduced in size, reduction in facial and body hair, feminine habitus and a high pitched voice (Fig. 1.10).
Q.48 What is Turner's syndrome?
The incidence is one in 3000. Females are affected. The karyotype is 45 XO. There is primary hypogonadism in females thought to be due to the absence of one chromosome. The clinical features are short stature due to growth retardation, webbing of the neck, increase in the carrying angle of the lower extremity known as cubitus valgus, low posterior hair line, far placed nipples, cardiac defects, arched palate, lymphedema of hands and feet, absence of secondary sexual characters, infantile genitalia, inadequate breast development, and streak-ovaries.
The defects are as outlined below:
- accessory thyroid
- thyroid crypt sinus
- ectopic thyroid
Accessory thyroid can occur along the path of the thyroglossal duct and it is in association with the normal thyroid gland. It is usually seen at the foramen cecum. The foramen cecum never opens on the skin. Ectopic thyroid is very rare and if it is present, it is below the hyoid bone.
Q.50 How is a tooth developed?
The enamel of the tooth develops from ameloblast and the dentin develops from odontoblast. The enamel is an ectodermal derivative whereas the dentin is mesodermal in origin.
Q.51 How does the lacrimal gland develop?
This develops by 25 mm stage as a small epithelial bud from the ectoderm.
Q.52 What is “x-zone” in the suprarenal gland?
The primitive cortex is the x-zone.
Q.53 How does the suprarenal gland develop?
It develops in two parts. The cortex develops from the mesoderm and medulla develops from the sympathetic cells.
Q.54 Why is the suprarenal relatively larger than the size of kidney in the fetal life?
This is due to big acidophilic cells in the cortex which become basophilic in the postnatal life.
Q.55 What is Gartner's duct?
The mesonephric ducts in females will disappear normally. If they persist in the postnatal life then this condition is known as Gartner's duct, which is attached to the labia majora.
Q.56 Name the three parts of urogenital sinus?
- Vesicoureteral part
- Pelvic part
- Phallic or penile part.
Q.57 What is harelip and its cause?
There is non-fusion in the upper lip either on one or both sides. This is a developmental defect, where the frontonasal process does not fuse with the maxillary process (unilateral harelip or bilateral harelip) (Fig. 1.11).
Histology
Q.58 What is podocyte?
The Bowman's capsule's visceral layer cells are large with foot like processes, whose cytoplasm projects into the capsular space. These are podocytes. The space in between the processes is 0.02–0.04 mm.
Q.59 What are the different types of cells in the tubules of the kidney?
The proximal convoluted tubule is formed of a single layer of low columnar cells with rounded nucleus and granular cytoplasm, stained deeply by eosin. The straight proximal or medullary portion more or less looks like the cortical portion. The loop of Henle has flattened epithelial cells with nuclei bulging into the lumen with abundance of cytoplasm. The thick ascending loop is lined by cuboidal cells.
Q.60 What is spermiogenesis?
The process of transformation of spermatids to spermatozoa is called spermiogenesis.
Q.61 Why does the esophagus have stratified squamous epithelium?
The reason for the above is to enable the wear and tear secondary to the swallowing of hard food.
Q.62 Why does the transitional epithelium line the bladder?
This is to help to withstand the action of chemicals in the bladder.
Q.63 What is duct of Bellini?
It is the main collecting duct which is located in the medulla of the kidney into which a number of the collecting tubules drain urine.
Q.64 What is the space of Disse?
This space is in between the Kupffer cells of liver (which lines the sinuses) and hepatic cells, and it is traversed by reticular fibers.
Q.65 What are centroacinar cells?
These cells are noticed in the lumen of the pancreatic acini.
Q.66 What are interstitial cells?
The interstitial cells are those which are in the connective tissue of the testis, in between the seminiferous tubules, and they are also known as Leydig cells.
Q.67 What is the purpose of simple squamous epithelial lining in certain areas of the body?
The main purpose of this epithelium is for passive transport of gases or fluids. It lines the pleura, pericardium and the peritoneum.
Q.68 What is the difference between the stratified squamous epithelium and transitional epithelium?
The transitional epithelium has similar cells whereas the stratified epithelium has cells of different shapes and morphology.
Q.69 What cellular change occurs during the distended and contracted phases of the bladder?
During the contracted phase the cells look like cuboidal or columnar cells and numerous layers of epithelium are present. During the distended state the layers are reduced and the superficial cells are flattened.
The basement membrane is well developed and makes an even contour.
Q.71 What are rectal columns or columns of Morgagni?
These are seen in the rectum, formed of submucosa and mucosa. The mucosa is formed by columnar epithelium, lamina propria, muscularis mucosae and lymphocytes.
Q.72 What are concretions?
They are the calcified organic material found in the alveoli of the prostate gland.
Q.73 What is Bowman's membrane?
This is found in the cornea. It is a homogenous membrane on which the epithelium of the cornea rests and it stops at the limbus.
Q.74 What is Descemet's membrane?
This is also found in the cornea, and is also called as the posterior elastic lamina. It is a transparent elastic membrane, and on it rests the endothelium of the cornea.
Q.75 What are rods and cones?
These are specialized cells, homologous with the ependymal cells of the ventricular cavity which are present in the outer nuclear layer of the retina. They are photosensitive receptor cells.
Q.76 Where do you get the pseudostratified columnar ciliated epithelium?
The epithelium is present in the trachea and bronchi. It is characterized by the presence of nuclei which are arranged at different layers.
Q.77 What is stratified squamous epithelium and where do you find it?
It is seen in the esophagus, where it is a non-cornified and the skin where it is a cornified epithelium. The cells are arranged in a different fashion and are mostly squamous type of cells. The intermediate cells are polyhedral with rounded and oval nuclei. In these cells the mitotic division can also be seen sometimes. The deeper layer of cells can be cuboidal or columnar. The cytoplasm of the deeper cells is granular and is rich in chondroitin, with oval nuclei. The basement membrane is rarely visible.
Q.78 What is the structural unit of bone?
Osteon or “haversian system” is called the structural unit of a bone, each system consists of a haversian canal surrounded by concentric lamellae.
Q.79 What is a cement line?
This is a refractive line forming the boundary of each osteon.
Q.80 What type of collagen does hyaline cartilage consist of?
Hyaline cartilage consists primarily of type II collagen.
Q.81 What is the difference between the cardiac and striated muscle?
The striated muscles have the nucleus in the periphery and the striations are better visible, whereas in the cardiac muscle, the nucleus is centrally positioned and the fibers are branched.
Q.82 What is the structure of the gallbladder?
The gallbladder has mucous membrane which is thrown into folds and has numerous mucous cells. The tall columnar cells lines the lamina propria.
Q.83 What is the structure of pancreas?
The lobules of the pancreas are covered by a loose connective tissue and there is no definite capsule present. The alveoli are lined by pyramidal cells having a basement membrane. The inner part of the cell have secretory granules, whereas, the outer part have staining capacity to basophilic dye. The islets of Langerhans are present between the alveoli which are responsible for producing insulin. They vary in number from 1/2 million to 1 million. They are highly vascular having “A”, “B” and “D” cells.
Q.84 What is respiratory bronchi's structure?
Respiratory bronchi have cuboidal epithelium, goblet cells and these cells lack cilia.
Q.85 What is the histology of trachea?
It is formed by the respiratory epithelium or pseudostratified columnar ciliated epithelium with goblet cells. The lamina propria has glands which form the secretions that are released into the epithelium. The longitudinal fibers present on the external surface with the transverse fibers form a very definite layer known as trachealis muscle.
Q.86 What is the structural differences between the interlobular, intralobular and respiratory bronchiole?
- Interlobular bronchus have respiratory type of epithelium, smooth muscle fibers (reiseeineres muscle) and plates of cartilage.
- Intralobular bronchus has a stellate lumen, columnar ciliated epithelium and goblet cells.
- Respiratory bronchi have cuboidal epithelium, goblet cells but lack cilia.
Q.87 How does the trachea extend longitudinally during inspiration?
This is due to the yellow elastic and white collagenous fibers which are enclosed by fibrous membrane and extend during respiration.
Q.88 What is the histology of the urinary bladder?
The bladder has four layers which are:
- The outer layer which is the serous layer, formed by the peritoneum covering the superior surface of the bladder
- The muscular layer has three layers namely: external, middle and internal layers which are arranged like bundles
- The submucous layer with areolar cells which have elastic fibers
- The mucous layer, formed of transitional epithelium.
Q.89 What is the histology of urethra?
- The prostatic part is lined by transitional epithelium
- The membranous and spongy part is lined by the stratified columnar epithelium
- Fossa navicularis is lined by stratified squamous epithelium.
Q.90 What are vaginal rugae?
The mucous coat of the vagina is corrugated by elevations and they are known as the rugae.
Q.91 What is the difference between the normal and lactating mammary gland?
The normal mammary gland is formed by the ducts and fibroareolar tissue. The alveoli are small and few in number, whereas, during the pregnancy the alveoli are enlarged and distended and there are increased number of ducts.
Q.92 What are the layers forming the vagina?
The layers forming the vagina are mucous and the muscular coats. The mucous coats have folds or rugae whereas the muscular coats have plain muscle fibers, disposed longitudinally. The lower ends of the vagina have circular fibers bundles of striated muscle. The vaginal rugae are covered by stratified squamous epithelium.
Q.93 What is the structure of the thyroid gland?
The thyroid gland has lobules. The acini are lined by cuboidal cells and have colloid material in the center.
It is differentiated by the presence of epithelial cells interconnected with trabeculae which are less vascular.
Q.95 How does the thymus looks under the microscope?
The lobules have a cortex and medulla. The cortex has lymphocytes embedded in the fibrous reticulum but has no lymph vessels. The medulla is differentiated by the presence of reticular cells and lymphocytes. The most important structure present in the medulla is known as the Hassall's corpuscles, these are concentric epithelioid cells varying in size between 25 and 75 mm in diameter.
Q.96 What are the types of cells seen in the pituitary gland?
There are two lobes present in the pituitary gland, the anterior and posterior lobes. The anterior lobe is lined by the chromophobes and chromophils. The chromophil cells could be acidophils or basophils. The basophils form 1/3 of the total number of cells whereas the acidophils form 1/10 of the total cells. The pars posterior has neuroglial cells and pituicytes which produce oxytocin which causes uterine contraction.
Q.97 How would you identify the vas deferens?
The vas deferens has a small irregular lumen with ciliated columnar epithelium or pseudostratified epithelium. It is highly muscular having outer longitudinal and inner circular fibers. The lamina propria surrounds the lumen.
Q.98 How will you identify the prostate gland?
The presence of fibromuscular stroma that is the connective tissue in between the alveoli is the characteristic histologic feature of the prostate gland. The alveoli are lined by columnar epithelium and the ducts are stained darkly. The alveoli have calcified organic material called corpora amylacea present in them.
Q.99 What is the difference between the testis and the epididymis?
The testis and epididymis both have basement membranes. The testis is lined by specialized epithelial cells, whereas, the epididymis is lined by ciliated columnar cells, and clusters of spermatozoa are also present. The testis is enclosed by a thick connective tissue known as “tunica albuginea”.
Q.100 What are the different layers of the ovary?
The outermost layers are formed by the theca externa and theca interna. The ovarian follicles are surrounded by zona pellucida and externally have follicular cells known as corona radiata. The maturing sex cells and corona radiata are known as cumulus oophorus and in case they are stained deeply, they are known as “call-exnervacuoles”. The nucleus lies inside the zona pellucida.
Q.101 What constitutes the lacrimal gland?
This is formed by the acini with serous cells. Depending on the function, the size of the lumen changes. The ducts have a double layer of prismatic cells.
Q.102 What is the histology of the iris?
It is a mass of stroma formed by elastic fibers along with the pigmented cells, plain muscle fibers and blood vessels.
Q.103 What is the structure of the eyelid?
It has a firm plate of condensed fibrous tissue known as tarsus. The skin is lined by stratified squamous epithelium and has a muscular layer internally.
Musculoskeletal System (Fig. 1.12)
Osteology
Q.104 What are the subdivisions of skeleton?
The skeleton is divided into:
- Axial skeleton: It is central bony frame-work, e.g. skull, vertebral column and thoracic cage.
- Appendicular skeleton: Formed by peripheral bones of the limbs.
Q.105 How the bones are classified according to shape?
- Long bones: Characterized by elongated tubular shaft, having a central medullary cavity and expanded articular ends (epiphyses), e.g. humerus, radius, femur, etc.
- Smaller long bones: They have only one epiphysis, e.g. metacarpals, metatarsal.
- Short bones: They are cuboid, cuneiform, scaphoid or trapezoid in shape, e.g. carpal and tarsal bones.
- Flat bones: Like shallow plates, e.g. ribs, scapula and bones of cranial vault.
- Irregular bones: Includes those bones which cannot be assigned to any of above groups, e.g. hip bone, vertebrae, etc.
- Pneumatic bones: They contain air spaces and are lined by mucous membrane, e.g. maxilla.
- Accessory bones: These are sometimes present in relation to limbs and skull bones.
Q.106 What are the functions of the bones?
- Provide shape and size to body
- Provide attachment to muscles, ligaments and tendons
- Protect vital organs
- Resist compression and tension stresses due to collagen tissue in bones
- Act as store house for calcium and phosphorus
- Act as a system of levers for movements by muscles
- Ear ossicles help in audition
- Bone marrow has blood forming function
- Reticuloendothelial cells of marrow are phagocytic and have a role in immune reactions
- Air sinuses in skull provide resonance to the voice.
Q.107 What are sites where red bone marrow is present in adults?
Proximal ends of femur and humerus, ribs, sternum, skull, vertebrae and hip bone.
Q.108 What is anthropometry?
It is the study of variation in dimensions and bodily proportions of various bones in different races and with age and sex in a single race.
Q.109 What are the parts of long bone?
- Epiphysis: Ends of a long bone which ossifies from secondary centers.
- Metaphysis: The epiphysial ends of diaphysis. It is the zone of active growth of bone.
- Epiphysial plate of cartilage: It separates metaphysis and epiphysis. Proliferation of this cartilaginous plate leads to lengthwise growth of bone.
Q.110 What are the different types of epiphyses?
- Pressure epiphysis: Articular end takes part in transmission of weight, e.g. head of femur, lower end of radius, and medial end of clavicle.
- Traction epiphysis: Non-articular. One or more tendon is attached to it which exerts a traction on it, e.g. trochanters of femur.
- Atavistic epiphysis: Phylogenetically represents a separate bone which in man has become fused to another bone, e.g. coracoid process of scapula.
- Aberrant epiphysis: These are not always present, e.g. epiphysis at head of first metacarpal.
Q.111 How the bones are classified according to their structure?
- Compact bone: Dense and is developed in cortex of long bones. It is able to resist mechanical pressure.
- Cancellous bone (spongy): Consists of meshwork of trabeculae (lamellae) within which are intercommunicating spaces, e.g. vertebral bodies, ribs, and sternum.
Q.112 What are Sharpey's fibers?
These are the transverse fibers which hold the lamellae of the compact bone together and periosteum to the underlying bone.
Q.113 What are the different types of lamellae in a bone?
- Circumferential lamellae: Lie parallel to bony surface
- Osteonic lamellae: Concentric lamellae found around vascular canals of bone.
- Interstitial lamellae: Lie in space between osteons, i.e. vascular canals.
Q.114 How the bones are classified according to their developmental origin?
- Intramembranous (dermal) bone: Develops from direct transformation of condensed mesenchyme, e.g. bones of skull.
- Intracartilaginous (endochondral) bone: Replaces a preformed cartilage model, e.g. bones of limb and thoracic cage.
- Membranocartilaginous bone: Develops partly in membrane and partly in cartilage, e.g. clavicle and mandible.
Q.115 What is Wolff's law?
The mechanical stresses are directly proportional to the bone formation.
Q.116 What are centers of ossification?
These are certain constant points in a bone where the mineralization of connective tissue begins and the process of transformation spreads, until whole skeletal element is ossified.
Q.117 What is ‘law of ossification’ for a long bone?
Where a bone has an epiphysis at either end, the epiphysis which is first to appear is last to join and the epiphysis which is last to appear is the first to join except fibula.
Q.118 What is the arterial supply of a long bone?
The arterial supply of a long bone is derived from four sources:
- Nutrient artery: It enters the shaft through nutrient foramen and runs obliquely in cortex and divides into ascending and descending branches in medullary cavity. Each branch inturn divides and redivides into parallel vessels, which run in metaphysis.
- These terminate by anastomizing with epiphyseal, metaphyseal and periosteal arteries.
- It supplies medullary cavity and inner 2/3 of cortex.
- The nutrient foramen is directed opposite to the growing end of bone.
- Juxta-epiphyseal (metaphyseal) arteries of Lexer: These are derived from anastomosis around the joint. They pierce the metaphysis along line of attachment of joint capsule.
- Epiphyseal arteries: Derived from periarticular vascular arcades found on non-articular bony surface.
- Periosteal arteries: These ramify beneath periosteum and supply outer 1/3 of cortex.
Q.119 What are ‘sesamoid bones’? What are their characteristic features?
- These are bone nodules found embedded in tendons where they lie close to articular surface or turn around a bony surface and joint capsules.
- These have no periosteum.
- They are not always completely ossified and consist of fibrous tissue, cartilage and bone in varying proportion, e.g. in tendon of adductor pollicis and flexor pollicis brevis and in 70% cases in tendons anterior to metacarpophalangeal joint; patella; in tendon of flexor hallucis brevis, peroneus longus and tibialis posterior.
- They ossify after birth.
- They have no Haversian system.
Q.120 What are the functions of sesamoid bones?
- Alter the direction of pull of muscle or improve the pull of the muscles.
- To minimize friction.
- To modify pressure.
- Aids in maintaining the local circulation.
- Provide additional articular surface to a joint.
Cartilage
Q.121 What is cartilage and what are its characteristic features?
- It is a type of connective tissue, which has gel like ground substance known as matrix in which are embedded cartilage cells (chondrocytes).
- The matrix is made up of mucopolysaccharide and contains elastic or collagen fibers.
- The cartilage is firm in consistency and has elasticity.
- It has no lymphatics or blood supply.
- It may become calcified.
Q.122 What are the different types of cartilage and their distribution?
- Hyaline cartilage: No fibers seen in matrix. Does not regenerate because chondrocytes cannot redivide. Present at articular surface of synovial joint bones, costal cartilage, bronchial cartilage.
- Fibrocartilage: Collagen fibers present in matrix. Present in intervertebral disk, disks in joints, and on the articular surfaces of clavicle and mandible.
- Elastic cartilage: Elastic fibers present in cartilage, e.g. auditory tube, pinna, and epiglottis.
Q.123 Name the cartilages which calcify.
- Hyaline cartilage
- Fibrocartilage
Q.124 How the different cartilages obtain their nourishment?
Fibrocartilage is supplied by blood vessels but hyaline and elastic cartilage have no capillaries and their cells are being nourished by diffusion of lymph.
Arthrology
- Fibrous joint: Bones are joined together by fibrous tissue. These joints are immobile or permit only slight movement.
- Cartilaginous joint: Bones are joined together by cartilage.
- Synovial joint: Articular surfaces of bone are covered by articular (hyaline) cartilage and between articular surface is joint cavity, containing synovial fluid. These joints permit maximum degree of movement.
Q.126 What are the different types of fibrous joints?
- Sutures: Found in skull and are immobile. Sutural ligament is present between two bones, which is attached on outside to pericranium and endocranium (outer layer of dura mater) on inside.
- Syndesmosis: Bones are connected by interosseous ligament, e.g. inferior tibiofibular joint.
- Gomphosis: Peg and socket type of joint, e.g. tooth in its socket.
Q.127 What are the characteristic features of synovial joint?
- Bony articular surfaces are covered with hyaline cartilage. It is insensitive to pain.
- Articular bones are connected by a fibrous capsule. The capsule has poor blood supply and heals very slowly. It is sensitive pain and stretch.
- Inner surface of capsule and all intra-articular structures which are not covered with cartilage are covered by synovial membrane, which secretes synovial fluid. It is highly vascular.
Q.128 What is the characteristic feature of synovial fluid?
It is presence of large amounts of mucopolysaccharide (hyaluronic acid) which gives it characteristic viscosity and it does not clot.
Q.129 What are the functions of synovial fluid?
- Lubrication of joint
- Nourishes the articular cartilage.
Q.130 What are the different types of synovial joint?
- Arthrodial (plane): Flat surfaces are in contact. Only gliding movement is possible, e.g. intercarpal joints, intertarsal joints.
- Hinge: Movements take place around a transverse axis, e.g. elbow joint between humerus and ulna.
- Pivot: A bony pivot like process moves within a ring. So movements are possible only around longitudinal axis through center of pivot, e.g. upper radioulnar joint and median atlantoaxial joint.
- Condylar: Two convex condyles (articular surface) moves within two concavities on opposite side. Movements occur mainly in transverse axis but partly in vertical axis (rotation), e.g. knee joint, temporo-mandibular joint, interphalangeal joints.
- Ellipsoid: Formed by a oval convex surface and an elliptical concavity, e.g. radiocarpal joint (wrist joint), metacarpophalangeal joint. Movements possible are flexion, extension, abduction, adduction and circumduction. No rotation occurs around central axis.
- Saddle: Articular surfaces are both concavoconvex. Movements permitted are same as in condylar type with some rotational movements, e.g. carpometacarpal joint of thumb, ankle joint.
- Ball and socket: Articular surfaces are globular head which fit into a cup like cavity. Movements are possible in every direction around a common center, e.g. hip joint, shoulder joint.
Q.131 What is a compound joint?
When more than two bone ends are enclosed with in a single capsule, the joint is known as compound, e.g. elbow joint has humeroulnar, humeroradial and superior radioulnar joint.
Q.132 What is a complex joint?
The joint cavity is divided completely or incompletely into two parts by intra-articular disk or fibrocartilage, e.g. temporomandibular joint, sternoclavicular joint and knee joint.
Q.133 How the joints are divided according to axis of movements?
| : Ball and socket joints : Ellipsoid and saddle joints : Hinge and pivot joints |
Q.134 What are fatty pads? What is their importance?
These are found in some synovial joints, occupying spaces where bony surfaces are incongruous and are covered by synovial membrane, e.g.
- Hip joint (Haversian fat pad)
- Talocalcaneonavicular joint
- Infrapatellar fold and
- Alar folds of knee joints.
Q.135 What are different types of cartilaginous joints?
- Primary (synchondroses): The related bones are united by hyaline cartilage. They are immovable and the cartilage is replaced by bone with age, e.g. costochondral joints, joint between epiphysis and diaphysis of a growing long bone, between sphenoid and temporal bones.
- Secondary (symphysis): These joints occur in median plane. The bone ends are covered by hyaline cartilage and are connected by a disc of fibrocartilage, e.g. manubriosternal joints, symphysis pubis, intervertebral joint between vertebral bodies. These do not disappear with age. Slight movement is possible.
Q.136 Why symphysis menti, joining two halves of mandible is not a true symphysis?
Because it disappears with age.
Q.137 What are the different intra-articular structures present in joints?
Cartilaginous structures:
- Articular disk
- Complete: Mandibular joint and strenoclavicular joint
- Incomplete: Acromioclavicular joint.
- Articular menisci: Semilunar cartilages of knee joint.
- Labrum glenoidale: Glenoid cavity of scapula and acetabulum.
- Ligaments traversing joints: Bind articular surfaces, e.g. ligamentum teres of hip joint, cruciate ligaments of knee joint.
Muscle tendons: These arise inside capsule of joint, e.g.
- At shoulder joint, long head of biceps
- At knee joint, tendon of popliteus.
Q.138 What are the functions of intra-articular disks?
- They act as a buffer and absorb shock.
- They strengthen the joint
- They make the articulation between bony surfaces smooth and harmonious.
Q.139 What is Hilton's law?
- A joint is supplied by the same nerves which supply the muscles crossing the joint and skin over the joint.
- Therefore, in joint diseases, irritation of nerves cause reflex spasm of muscles and referred pain to the overlying skin.
Q.140 What are the distinguishing features of different types of muscle?
Features | Smooth muscle | Skeletal muscle | Cardiac muscle |
|---|---|---|---|
Location | Found in viscera and blood | Found attached to skeleton vessels | Found in myocardium of heart |
Nerve supply | Autonomic nerves, so they are involuntary | Somatic nerves, so they are involuntary | Autonomic nerves, so they are involuntary |
Muscle fiber | Has no cross striations Each fiber is elongated, spindle shaped | Has cross striations Cylindrical cell | Has cross striations Muscle fiber show branches and anastomoses with neigh bouring fibers |
Single central nucleus | Multiple peripheral nuclei | Single central nucleus | |
Rhythmicity | Present | Absent | Present |
Automaticity | Present | Absent | Present |
Q.141 How the skeletal muscles are classified according to direction of muscle fibers?
- When the fasciculi (groups of muscle fibers) are parallel to line of pull, e.g.
- Strap like: Sternohyoid, sartorius.
- Fusiform: Biceps
- Quadrilateral: Thyrohyoid.
- When the fasciculi are oblique to line of pull, e.g.
- Triangular: Temporalis, adductor longus.
- Pennate (Feather like):
- Unipennate: Extensor digitorum longus, flexor pollicis longus.
- Bipennate: Rectus femoris
- Multipennate: Deltoid, subscapularis
- Circumpennate: Tibialis anterior.
- When muscle fibers are arranged in a twisted manner, e.g. trapezius, pectoralis major.
Q.142 What is the nerve supply of skeletal muscle?
Supplied by somatic nerves.
- Motor fibers: Has
- Alpha efferents: Myelinated anterior horn motor neurons, supply muscle fibers.
- Gamma efferents: Myelinated fibers, supply muscle spindle (sensory end organ of skeletal muscle).
- Autonomic efferents: Non-myelinated, supply smooth muscle fibers of blood vessels.
- Sensory fibers:
- Myelinated fibers: Distributed to muscle spindle, tendon and fascia of the muscle.
- Non-myelinated fibers: Distribution not known.
Q.143 What is a ‘motor unit’?
It is a functional subdivision of muscle. It includes a single alpha motor neuron together with muscle fibers which it innervates.
Q.144 What is myotome?
A myotome is amount of muscle supplied by one segment of the spinal cord and muscles sharing a common primary action on a joint irrespective of their anatomical situation are supplied by the same segments.
Q.145 What are the features of muscles which receive ‘double innervation’?
Generally they are flexor muscles that receive nerve supply from the extensor compartment. These muscles develop in the extensor compartment of fetal limb but for functional reasons, come to lie in the flexor compartment of the adult limb, bringing its nerve supply with, e.g.
- Lateral portion of brachialis (supplied by radial nerve).
- Short head of biceps femoris (by personal part of sciatic nerve).
- Brachioradialis (by radial nerve).
Q.146 What are bursae and where they are found?
Bursae are sacs of synovial membrane supported by dense irregular connective tissue.
They are found at the places where structures which move relative to each other are in tight apposition, e.g.
- Between skin and bone (Subcutaneous bursae)
- Between muscle and bone, tendon or ligament (Submuscular).
- Between fascia and bone (Subfascial)
- Between ligaments (Interligamentous)
- Adventitious bursae: Normally not present but develop over bony situations which are subject to much friction or pressure, e.g.
- Tailor's ankle: Above lateral malleolus a bursa appears in tailors, who sit in cross legged position, thus bringing this area in contact with table.
- Porter's shoulder: In porters, between upper surface of clavicle and skin.
- Weaver's bottom: Between gluteus maximus and ischial tuberosity.
Q.147 What is ‘aponeuroses’?
These are flat sheets of densely arranged collagen fibers associated with the attachment of muscle.
Q.148 What are the different types of muscles according to their action?
- Prime movers: These are active in initiation and maintenance of a particular movement.
- Antagonists: Muscles which oppose prime movers or initiate and maintain its converse.
- Fixators: Stabilize the position of a joint to provide a fixed base on which other muscles can act.
- Synergists: These help the prime movers in bringing the movement. They eliminate the undesired actions when prime movers cross more than one joint.
Circulatory System
Q.149 What is the difference between arteries and veins?
Features | Arteries | Veins |
|---|---|---|
Thickness | Thick walled | Thin walled |
Valves | Absent | Present |
Lumen | Narrow | Larger |
Fibromuscular tissue | More | Less |
Elasticity | More | Less |
Arteries carry oxygenated blood except pulmonary artery and veins carry deoxygenated blood except pulmonary veins.
Q.150 What are the differences between capillaries and sinusoids?
Features | Capillary | Sinusoid |
|---|---|---|
1. Lumen | Smaller, regular | Larger (up to 30 m) irregular |
2. Structure | Endothelial lining: | |
Continuous | May be incomplete; some phagocytic cells are present. | |
Basal lamina: | ||
Thicker and surround endothelial cells Adventitial support: Present | Thinner Absent | |
3. Location | Connect metaarterioles and venules | Connect arteriole with venule or venule with venule |
Q.151 Name the structures where fenestrated capillaries are present.
- Pancreas
- Intestine
- Renal glomeruli
- Endocrine glands
- Skin
- Muscles
- Fascia
- Brain
Q.153 What is the nerve supply of an artery?
The arteries are supplied by sympathetic nerves via nervi vasorum. These are vasoconstrictor. Few myelinated sympathetic fibers are also present, which carry pain sensation.
Q.154 Name the sites where sinusoids are present.
- Suprarenal gland
- Carotid body
- Liver
- Spleen.
Q.155 What are ‘anastomosis’?
Arteries do not end always in capillaries, they unite with one another forming anastomosis.
Q.156 What are the different types of anastomosis?
- Actual: Arteries meet end to end, e.g. labial branches of facial arteries, intercostal arteries, uterine and ovarian arteries, arterial arcades in mesentery, arteries of greater and lesser curvatures of stomach.
- Potential: Anastomosis is by terminal arterioles and given sufficient time the arterioles can dilate to take sufficient blood, e.g. coronary arteries, cortical arteries of cerebral hemispheres, anastomoses around joints of extremities.
Q.157 What are the functions of anastomosis?
- Equalization of pressure over territories which they connect.
- Provide collateral circulation when a vessel is interrupted.
Q.158 What are ‘end arteries’? What is their importance?
These are arteries which have no anastomoses with their neighbors, e.g. central artery of retina, arteries of spleen, liver, kidneys, metaphyses of long bones, medullary branches of the central nervous system, coronary arteries.
Importance: If an end artery is occluded, necrosis (death) of tissue takes place in area supplied by the vessel.
Q.159 What are ‘arteriovenous shunts’?
These are vessels of communication between arteries and veins and when open, they bypass the capillaries, e.g. in skin of nose, lips and external ear, mucous membrane of alimentary canal, thyroid gland, palmar skin.
Q.160 What are the functions of arteriovenous shunts?
- Regulate the regional blood flow
- Regulate blood pressure
- Pressor reception
- Regulation of the temperature.
Lymphatic System
Q.161 What are the components of lymphatic system?
- Lymph vessels: Formed by lymph capillaries.
- Peripheral lymphoid tissue: Spleen, epitheliolymphoid system, lymph nodes and lymph nodules.
- Central lymphoid tissue: Bone marrow and thymus.
- Lymphocytes: Circulating in vessels.
Q.162 How the lymph capillaries differ from blood capillaries?
Lymph capillaries have
- Bigger lumen
- Lumen is less regular
- Permeable to bigger molecules
- Form pathways for absorption of colloid from tissue spaces
Q.163 Name the sites were lymph capillaries are absent.
- Epidermis
- Hair
- Nails
- Cornea
- Articular cartilage
- Splenic pulp
- Spinal cord
- Brain and
- Bone marrow
Q.164 What is the structure of lymph trunk?
It consists of three coats:
- Tunica adventitia: Composed mainly of fibrous tissue and some smooth muscle fibers.
- Tunica media: Consists of smooth muscle cells, fibers of which are arranged circularly and separated from one another by fibrous tissue.
- Tunica intima: Consist of endothelial cells and fibrous tissue.
- They possess more number of valves than small veins. The valve consists of reduplicated endothelium and lumen of lymph vessel immediately proximal to valve is expanded into a sinus, which gives the vessel a beaded appearance.
Q.165 What are the factors which favor the propulsion of lymph from tissue spaces towards lymph nodes and venous blood stream?
- In tissue spaces, filtration pressure generated by filtration of fluid from blood capillaries.
- Concentration of surrounding muscles compressing lymph vessels.
- Pulsation of artery near lymph vessels.
- Respiratory movements.
- Negative pressure in brachiocephalic veins.
- Contraction of smooth muscle of vessel.
Q.166 What is the function of lymph capillaries?
Lymph capillaries are concerned with the absorption of fluid from tissue spaces.
Q.167 What is structure of lymph node?
Grossly: These are oval bodies situated in the course of lymph vessels. The blood vessels enter and leave node at the hilus. A lymph node has a cortex into which afferent vessels drain and a medulla from which efferent vessels arise.
Microscopic:
- Capsule and trabeculae: Composed of collagen fibers, fibroblasts and elastic fibers.
- Reticulum: Fibrocellular and forms a meshwork within spaces outlined by capsule and trabeculae. In medulla, fewer cells in loose reticulum are present. Such parts allow rapid passage of lymph and are termed lymph sinuses. Reticular fibers are thin collagen fibers, ensheathed by fixed macrophages in an amorphous matrix. Reticular cells lining lymph sinuses are termed as littoral cells.
- Majority of cells are lymphocytes with some macrophages. In cortex, cells are densely packed to form lymphatic follicles. The central part of follicle has a germinal center, which consists of large cells. In medulla, cells are loosely packed.
The outer part of cortex has B-lymphocytes and inner part has T-lymphocytes. The medulla has mature B-lymphocytes, plasma cells and macrophages.
Q.168 What is epitheliolymphoid system and where it is found?
- These are collections of lymphoid tissue found under the epithelium.
- These are found in Peyer's patches in intestine, appendix, pharyngeal tonsil, palatine and lingual tonsil.
These cells are concerned with phagocytosis.
- Pericytes (Rouget cells) in capillaries
- Dust cells in lungs
- Macrophages in connective tissue, bone marrow and suprarenal gland
- Reticular cells in spleen and lymphoid tissue
- Monocytes in blood
- Kupffer cells in liver
- Microglia in nervous system.
Q.170 What are the functions of a lymph node?
- Act as a filter for lymph. Thus, foreign particles are prevented from entering the bloodstream.
- Macrophages in sinuses engulf foreign particles.
- Trapping of antigens by phagocytes
- Mature B and T lymphocytes are produced in the lymph node.
- Provides interaction between antigen laden phagocytes and lymphoid tissue with mounting of both cellular and humoral immune response.
- Provides portal of entry for blood borne lymphocytes back into lymphatic channels.
Nervous System
Q.171 What are the subdivisions of nervous system?
- Central nervous system: Includes brain and spinal cord.
- Peripheral nervous system: Divides into:
- Cerebrospinal nervous system: Includes 12 pairs of cranial nerves and 31 pairs of spinal nerves.
- Peripheral autonomic nervous system: Includes sympathetic and parasympathetic nervous system.
Q.172 What are the cell types forming nervous tissue?
- Neurons (Nerve cells): Excitable cells.
- Neuroglia: Non excitable cells, forming connective tissue of the nervous system.
Q.173 What is the function of neurons?
Reception, transmission, integration and transformation of impulses.
Q.174 What is the histological structure of a neuron?
Each neuron consists of:
- Cell body (Perikaryon): Mass of cytoplasm with a diploid nucleus and bound by a membrane. The cytoplasm contains basophilic Nissl bodies. Nissl body is made of ribonucleic acid and is concerned with the protein synthesis.
- Neurites: Extensions from periphery of cell body.
They are of two types:
- Dendrites: Conduct impulses towards cell body. May branch to form a dendritic tree.
- Axon: Conduct impulses away from cell body. Begins at axon hillock and terminate by dividing into axon terminals (telodendria).
Q.175 What are the different types of neurons?
- Unipolar: Single extension from cell body, e.g. mesencephalic nucleus of fifth cranial nerve.
- Bipolar: Extension at each end of the cell body, e.g. retinal bipolar cells, olfactory neuroepithelium and ganglion of 8th cranial nerve.
- Multipolar: Several extensions from cell body, e.g. most cells of brain and spinal cord.
- Pseudounipolar: Usually have one process arising are pole of cell body but actually two extensions emerge at same pole, .g. dorsal root ganglion of spinal cord.
Q.176 What are Amacrine cells?
These are small neurons present in retina, olfactory bulb which lack an obvious axon and permit conduction in either direction.
Q.177 What are the different types of neurons in brain?
- Stellate cells: Dendrites extend in all directions from cell body.
- Pyramidal cells: Cell body is conical in shape and dendrites extend from angles of cone or pyramid.
- Fusiform cells: Spindle shaped dendrites emerge at both ends.
- Glomerular cells: Dendrites at their tip are highly coiled.
Q.178 How transmission occurs across the synapse?
Due to the release of transmitters (neurochemicals) released into the synaptic cleft by presynaptic process, which cause the stimulation or inhibition of postsynaptic process.
Q.179 What are the different types of synapse?
- Excitatory synapse: Neurotransmitters released causes stimulation of post-synaptic neuron.
- Inhibitory synapse: Neurotransmitter released causes inhibition of postsynaptic neuron.
- Reciprocal synapses: Transmission between two processes occurs in either direction by staggered synaptic zones on each side of synaptic cleft.
Q.180 What are different types of neuroglial cells in brain and spinal cord?
- Macroglia: Larger cells, develop from neural plate. They are of following types:
- Astrocytes: Have a small cell body with dendrite like extensions.
- Oligodendrocytes: They have fewer cell processes.
- Pituicytes: In posterior pituitary
- Muller cells: In retina.
- Ependymal cells: Line the ventricles of brain and central canal of spinal cord
- Bergmann cells: In cerebellum.
- Microglia: Smallest glial cells. They have fine dendritic processes and flattened outlines. Develop from mesodermal tissue surrounding nervous system.
Q.181 What are the functions of glial cells?
- Act as mechanical support for nervous system.
- Act as insulators, separating neurons and their processes from each other. They prevent impulses from spreading in unwanted directions due to their non conducting nature.
- Act defensively by phagocytosing foreign material and cell debris.
- Help in regulating biochemical environment of neurons.
- Oligodendrocytes form myelin sheath in central nervous system.
- Ependymal cells take part in secretion, transport and uptake of cerebrospinal fluid.
- By proliferation, glial cells repair, by filling the gaps left by dead or degenerating neurons.
- They take up, store and metabolise the neurotransmitters.
Q.182 What are the different types of fibers in peripheral nerve?
Depending on diameter and rate of impulse conduction fibers in peripheral nerve are of three types:
- Type A: Subdivided into:
- Sensory (Afferent) fibers
- Motor (Efferent) fibers
- Type B: Preganglionic autonomic fibers
- Type C: Nonmyelinated, postganglionic autonomic fibers
Q.183 What are the factors on which conduction in myelinated fibers depend?
- Diameter of axon
- Thickness of myelin sheath
- Internodal distance between nodes of Ranvier
-
16
Area and character of axonal membrane.
Q.184 What are the non-nervous cells present in peripheral nervous system?
- Capsular cells: Present around cell body of sensory and autonomic ganglia.
- Schwann cells: Present around axons of peripheral nerves and form myelin sheath.
Q.185 What is the composition of myelin?
Myelin contains lipid and basic proteins but has less proteins than cell membrane.
Q.186 What are ‘incisures of Schmidt-Lanterman’?
Ans. These are oblique clefts in the myelin and provide conduction channels for metabolities into depths of myelin sheath and axon.
Q.187 What is the characteristic feature of distribution of sympathetic and parasympathetic nervous system?
All parts of body, whether somatic or visceral, receive a sympathetic supply.
But the parasympathetic supply has no somatic distribution but is wholly visceral, but does not innervate all viscera (e.g. suprarenal glands and gonads, which have only a sympathetic supply).
Q.188 What is the origin of autonomic nervous system outflow?
Sympathetic outflow emerges at T1 to L2 segments of spinal cord.
Parasympathetic outflow emerges from brain via 3rd, 7th, 9th and 10th cranial nerves and from S2-4 segments of spinal cord.
Q.189 To which gland the secretomotor nerves are sympathetic?
Sweat glands.
Q.190 Which cranial nerves contribute to the cranial parasympathetic outflow?
Preganglionic fibers from third, seventh, ninth and tenth cranial nerves.
Q.191 What is the neurotransmitter of autonomic nervous system?
- Noradrenaline is neurotransmitter of sympathetic system except at nerves ending for sweat gland and blood vessels of muscles, where neurotransmitter is acetylcholine.
- Acetylcholine is neurotransmitter of parasympathetic system.
Genitourinary System
Q.192 What is the gubernaculum?
It is a continuous mesenchymal condensation extending from the gonadal anlage to the sexually undifferentiated labioscrotal fold. This guides the descent of the testis into the scrotum in the male and the descent of the ovary into the deep pelvis in the female.
Q.193 What represents the gubernaculum in the female?
It is represented by the round ligament of the uterus and the ligament of the ovary.
Q.194 What are the contents of the deep perineal pouch?
The deep perineal pouch consists of the urogenital diaphragm, that is, the deep transverse perineal muscle and it is associated inferior and superior fascias, the external urethral sphincter, and the membranous urethra in the male.
Q.195 Why is the nerve responsible for back pain during menstruation?
This is because the visceral afferent fibers that mediate pain from the fundus and the uterine body travel along the sympathetic nerve pathways mediated via the hypogastric nerve and the lumbar splanchnics to reach the upper lumbar levels (Ll-L2) of the spinal cord.
Q.196 What is the normal posture of the uterus?
The normal posture of the uterus is that it is anteverted and anteflexed.
Q.197 What is the external urethral sphincter in a female consist of?
The external urethral sphincter in the female is a modified portion of the deep transverse perineal muscle of the urogenital diaphragm.
Q.198 What is the pelvic diaphragm? And what is its function?
The pelvic diaphragm comprises the levator ani and the coccygeus muscle and their associated fascia, and is shaped like an inverted cone and forms the floor of the abdominopelvic cavity. Its function is to suspend and support the pelvic organs as well as to provide the principal component for continence.
Q.199 What does a posterolateral episiotomy incise?
A posterolateral episiotomy involves incising the skin over the ischioanal fossa, the bulbospongiosus muscle, the superficial transverse perineal muscle and associated transverse neurovascular bundle, a portion of the deep transverse perineal muscle and associated fascial layers (urogenital diaphragm) and frequently the medial fibers of the pubovaginalis and puborectalis portions of the levator ani.
Q.200 What is the autonomic innervation of the penis and its functions?
The sympathetic innervation of the penis is through the pelvic plexus and is responsible for ejaculation. The parasympathetic innervation is responsible for erection.
Q.201 How is the uterus formed?
The uterus is formed by the fusion of two paramesonephric tubes.