Module 3 Flashcards
Location of Major Endocrine Organs
Major endocrine glands:
- Pituitary
- Pineal
- Thyroid/Parathyroid
- Adrenal
Organs containing endocrine cells: hypothalamus, skin,Thymus, Heart, liver, stomach, Small intestine, pancreas, kidney, ovary, testes, adipocytes
- Second messenger system of the body
- Uses chemical messages (hormones) that are released into the blood
- Hormones control several major processes
- Reproduction
- Growth and development
- Mobilization of body defenses
- Maintenance of much of homeostasis
- Regulation of metabolism
Endocrine System
- are produced by specialized cells
- Cells secrete __ into extracellular fluids
- Blood transfers __ to target sites
- regulate the activity of other cells
Hormones
4 Main Groups of Chemicals that Act as Hormone
- Protein/Glycoprotein - insulin, growth hormone, PTH
- Small Peptide Molecules - Vasopressin and products of enteroendocrine cells
- Amino Acid Derivatives - thyroxine, epinephrine and norepinephrine
- Steroid - derived from cholesterol like adrenal cortical hormone, ovarian and testicular hormones
Control of Hormone Release
- Hormone levels in the blood are maintained by negative feedback
- A stimulus or low hormone levels in the blood triggers the release of more hormone
- Hormone release stops once an appropriate level in the blood is reached
Endocrine glands are activated by other hormones
Hormonal Stimuli of Endocrine Glands
Changing blood levels of certain ions stimulate hormone release
Humoral Stimuli of Endocrine Glands
- Nerve impulses stimulate hormone release
- Most are under control of the sympathetic nervous system
Neural Stimuli of Endocrine Glands
Characteristics of Endocrine Glands
- The glands are ductless; thus, hormonal secretions are poured directly to the blood through the capillaries.
- The internal supporting framework is reticular tissue.
- Highly vascular, thus provided with rich capillary networks among and between groups of secretory cells.
- The capillaries are fenestrated type in which endothelial wall contains numerous pores or openings which are covered by very thin diaphragms.
Development of the Endocrine System
On the basis of their germ layer of origin, the endocrine glands may either be ectodermal, mesodermal or endodermal.
- Ectodermal in origin - Pituitary gland; Pineal gland; Adrenal medulla
- Mesodermal in origin - Adrenal cortex; Leydig cells of the testis; Theca interna cells of the ovary
- Endodermal in origin - Thyroid gland; Parathyroid gland; Islets of Langerhans; Parafollicular cells or C-cells
Development of the Pituitary Gland
This develops from two sources:
- Rathke’s pouch
- Ectodermal outpocketing of the stomodeum (future mouth)
- Gives rise to the ADENOHYPOPHYSIS - Infundibulum
- Downward extension of the diencephalon
- Gives rise to the NEUROHYPOPHYSIS
- Anterior wall of Rathke’s pouch gives rise to the Pars distalis and the Pars tubercles
- Posterior wall of Rathke’s pouch gives rise to the Pars intermedia
ADENOHYPOPHYSIS
- Pars nervosa (infundibular process)
- Infundibular stem (stalk)
- Median eminence of tuber cinereum
NEUROHYPOPHYSIS
- Also known as the hypophysis cerebri.
- The hypophysis is a pea-sized glandular organ lodged in the hypophyseal fossa of the sella tursica of the body of the sphenoid.
- It is connected by the infundibulum stalk to the base of the brain and is covered by a capsule of dense connective tissue.
PITUITARY GLAND
Divisions of the Hypophysis
- Adenohypophysis
- Anterior part derived from the Rathke’s pouch
- An outgrowth from the ectodermal roof of the primitive oral cavity - Neurohypophysis
- Posterior part developed as a downgrowth from the floor of the diencephalon
- Also known as the anterior pituitary
- Subdivisions:
- Pars distalis
- Pars intermedia
- Pars tuberalis
Adenohypophysis
- Largest subdivision of the adenohyphysis.
- The cells are grouped into 2 categories:
1. Chromophils
2. Chromophobes
PARS DISTALIS
Chromophils
2 types of cells based on affinity to stains
- Acidophils – secrete prolactin and growth hormone
- Basophils - secrete FSH, LH, TSH, ACTH
- Smallest and least numerous among the cells in the pars distills
- Since they are small, their nuclei lie close to each other; and their cytoplasm is scanty, thus hardly seen.
- These cells are referred to as reserve cells since some of them may differentiate into acidophils or basophils as the need arises
Chromophobes
Stimulates release of Thyrotropin (TSH)
Thyrotropin releasing hormone (TRH)
Stimulates release of FSH and LH
Gonadotropin releasing hormone (GnRH)
Inhibits release of both GH and TSH
Somatostatin
Stimulates release of GH
Growth hormone-releasing hormone (GHRH)
Inhibits release of Prolactin
Dopamine
Stimulates synthesis of pro-opiomelanocortin (POMC) and release of both B-lipotropin and ACTH
Corticotropin-releasing hormone
% Total cells: 50
Hormone produced: SOMATOTROPIN (GROWTH HORMONE)
Major Function: Stimulates growth in epiphyseal plates of long bones via insulin-like growth factors (IGF) produced in liver
Somatotrophs
% Total cells: 15-20
Hormone Produced: PROLACTIN (PRL)
Major function: Promotes milk secretion
Lactotrophs or Mammotrophs
% Total cells: 10
Hormone Produced: FSH, LH, ICSH (Interstitial cell-stimulating Hormone)
Major Function: FSH promotes ovarian follicle devt and Estrogen secretion in women and spermatogenesis in men: LH promotes ovarian follicle maturation and Progesterone secretion in women and interstitial cell androgen secretion in men
Gonadotrophs
% Total cells: 5
Hormone Produced: THYROTROPIN (TSH)
Major Function: Stimulate TH synthesis, storage and liberation
Thyrotrophs
% Total cells: 15-20
Hormone Produced and Functions:
*ADRENAL CORTICOTROPIN (ACTH) - Stimulates secretion of adrenal cortex hormones
*LIPOTROPIN (LPH) - Helps regulate lipid metabolism
Corticotrophs
- It is found between the pars distalis and the infundibular process.
- It is characterized by the presence of follicles or cysts filled with colloid and lined by columnar epithelium, which are called RATHKE’S CYST.
- Also found are polygonal basophilic cells.
PARS INTERMEDIA
The hormone of the pars intermedia is the __, which causes the dispersion of melanin pigments in the melanoblast and increase the pigmentation of the skin.
melanocyte stimulating hormone (MSH)
- most highly vascular portion of the hypophysis.
- is formed of longitudinal columns or cords of cells that descend towards the pars distalis.
- The cell types are:
1. Undifferentiated cells
2. Small basophils and acidophils - There is NO HORMONE isolated in this area
PARS TUBERALIS
- It is formed of venules that connect the capillaries in the median eminence with the capillary sinusoids in the pars distalis. It is thru the HYPOPHYSEAL PORTAL CIRCULATION that the releasing hormones from the hypothalamus reach the secretory cells of the pars distalis.
- The neurohormones from the hypothalamus reach the pars distalis through nerve fibers.
- The blood supply of the hypophysis is derived from the SUPERIOR HYPOHYSEAL ARTERIES, branches of the internal carotid and branches of the posterior communicating arteries
HYPOPHYSEAL SYSTEM
- is formed of unmyelinated nerve fibers of the hypothalamo-hypophyseal tract, which are formed of axons of the neurons in the hypothalamic nuclei.
- The axons descend through the median eminence to the infundibular stalk and infundibular process.
neurohypophysis
Also found in the neurohypophysis, part of the pars nervosa, are the __ – cells with numerous processes and are considered as modified neuroglial cells.
pituicytes
(neurohypophysis)
- are small, spherical structures containing NEUROHORMONES ( ADH AND OXYTOCIN) stored in the PARS NERVOSA or in the infundibular process. These are neurosecretory materials secreted by the neurons in the hypothalamic nuclei and travel along the axons of these neurons to be stored and released from the axolemma of the nerve fibers.
Herring bodies
Hormones in the Pars Nervosa
Found in the infundibular process or pars nervosa (Posterior pituitary DOES NOT contain the cells that synthesize its 2 hormones)
- Pitocin (Oxytocin)
- Pitressin or ADH (Anti-Diuretic Hormone)
(pars nervosa)
- Synthesized by the paraventricular nuclei of the hypothalamus
- Stimulates uterine contraction and mammary gland
Pitocin (Oxytocin)
(pars nervosa)
- Synthesized by the supraoptic nuclei of the hypothalamus
- Increase water retention
Pitressin or ADH (Anti-Diuretic Hormone)
Development of the Thyroid Gland
- Develops from epithelial proliferation in the floor of the pharynx between the tuberculum impar and copula, at a point later indicated by the foramen cecum.
- It descends in front of the pharyngeal gut as a bilobed diverticulum. This is connected to the tongue by a narrow canal, the THYROGLOSSAL DUCT, which later disappears. The cystic remnants of the thyroglossal duct is called the THYROGLOSSAL CYST.
- The 5th pharyngeal pouch gives rise to the ULTIMOBRANCHIAL BODY, which later is incorporated in the thyroid gland. The cells of the ultimobranchial body give rise to parafollicular or C-cells of the thyroid gland secreting calcitonin.
- found in the anterior part of the neck, consisting of two lobes connected by a narrow ISTHMUS, which crosses the trachea just below the cricoid cartilage.
- has a CONNECTIVE TISSUE CAPSULE that is continuous with the surrounding cervical fascia. The outer capsule is loosely on its deep surface of another layer of moderately dense connective tissue that is intimately adherent to the gland.
Thyroid Gland
- The structural unit is the spherical cystlike follicles, which are lined by SIMPLE CUBOIDAL EPITHELIUM and containing a gelatinous COLLOID.
- This represents the stored product of secretory activity by the lining epithelium.
- The FOLLICULAR CELLS are surrounded by a thin basal lamina.
- The epithelial cells vary in height, but are commonly cuboidal, squamous when the gland is hypoactive and columnar when it is hyperactive.
- The nucleus is spherical, centrally located, poor in chromatin and contain one or more nucleoli
Thyroid Gland
(Thyroid Gland)
These were originally called __ based on their position, but with the discovery that they produce CALCITONIN, they are now called C-cells. Other names are LIGHT CELLS, MITOCHONDRIA-RICH CELLS AND ULTIMOBRANCHIAL CELLS
parafollicular cells
Functions of the Thyroid Gland
- Synthesize, store and release hormones concerned with the regulation of metabolic rate (TRI-IODOTHYROXINE OR T3 AND TETRA-IODOTYROXINE OR T4) by the follicular epithelial cells. (TH increase metabolic rate)
- Decrease blood calcium level by the C-cells or parafollicular cells through the secretion of calcitonin. (inhibits osteoclast activity)
Development of the Parathyroid Gland
It develops from:
- Superior parathyroid- Dorsal wing of the 4th pharyngeal pouches
- Inferior parathyroid - Dorsal wing of the 3rd pharyngeal pouches
- These are two pairs of glands which are small, yellow-brown oval bodies adhering to the posterior surface of the thyroid gland.
- A connective tissue capsule separates them from the thyroid gland.
- Delicate connective tissue septa partially divide the gland into poorly defined lobules and still finer ones separate the epithelial cells into anastomosing cords and groups.
PARATHYROID GLAND
PARATHYROID GLAND
The parenchyma is composed of two types of cells:
- PRINCIPAL OR CHIEF CELLS
- Constant occurrence
- Polyhedral cells with round nuclei, with loosely arranged chromatin giving a vesicular appearance, and basophilic cytoplasm - OXYPHIL CELLS
- Appears only at the end of the first decade of life until puberty
- Larger cells with smaller and darker nuclei and acidophilic cytoplasm
The parathyroid glands regulate __ concentration by stimulating resorption of bone and reabsorption of calcium ions from ultrafiltration of the kidneys and with the aid of the vitamin D absorption of calcium from the gut.
calcium
Through the principal cell secretion of parathyroid hormone (PTH), blood calcium level increases.( by stimulatng osteoclast activity)
Parathyroid gland
Development of the Adrenal Gland
Adrenal cortex
- About the 5th week of development, MESOTHELIAL CELLS proliferate and later differentiate into large acidophilic structures forming the primitive or fetal cortex of the adrenal gland
- Shortly later, a second wave of cells from the mesothelium penetrate and surround the original acidophilic mass. These cells will form the definitive cortex of the adrenal gland.
Adrenal medulla
- Arises from NEURAL CREST CELLS. These cells invade the medial aspect and become cords and clusters forming the medulla of the adrenal gland.
- The cells of the adrenal medulla are stained yellowish brown with chrome salts. Hence, they are called CHROMAFFIN CELLS.
- The paired glands are roughly triangular, flattened organs embedded in the retroperitoneal fat tissue at the cranial pole of each kidney.
- It has a thick capsule of connective tissue that extends into the cortex as trabeculae.
- There are two functionally and structurally distinct parts:
1. Cortex
2. Medulla
ADRENAL GLANDS
ADRENAL GLANDS
- The principal secretory cells of the MEDULLA ARE derived from the NEURAL CREST CELLS.
- The secretory cells of the CORTEX are derived from the MESODERMAL CELLS IN THE NEPHROGENIC RIDGE.
- The cortex forms the bulk of the gland.
- It has three distinguishable concentric zones:
1. Zona glomerulosa
2. Zona fasciculata
3. Zona reticularis
ADRENAL CORTEX
- Adjacent to the capsule is a narrow zone in which the cords of columnar cells are in ovoid groups.
- There is no central cavity within a cell group as in exocrine glands, but there is a rich network of blood vessels externally.
- It produces ALDOSTERONE
ZONA GLOMERULOSA
a potent mineralocorticoid causing water and sodium retention in exchange for potassium in the kidney.
ALDOSTERONE
- The middle and broadest zone is composed of cell cords coursing parallel to one another in radial direction toward the medulla.
- The secretory cells are cuboidal or polyhedral, and sometimes binucleated, which are vesicular.
- These cells secrete GLUCOCORTICOIDS , especially CORTISOL
ZONA FASCICULATA
- Network of cell cords, which are smaller than those of the fasciculata, darker nuclei, fewer lipid droplets and numerous lipofucshin granules.
- Also produce CORTISOL but primarily secrete Weak Androgens including DEHYDROEPIANDROSTERONE (DHEA) – precursors for testosterone and Estrogen
- It is probable that the outer part of the fasciculata produces much of the cortisol in unstressed individuals.
ZONA RETICULARIS
- the most important glucocorticoid, has a protein wasting effect and promotes gluconeogenesis; suppress immune cell activities
Cortisol
- The secretory cells ( Chromaffin cells) here are in anastomosing groups associated with blood vessels.
- The parenchymal to columnar, and contain cytoplasmic granules, which become brown when oxidized by potassium bichromate.
- The chromaffin reaction of the granules is due to their content of CATECHOLAMINES – EPINEPHRINE AND NOREPINEPHRINE.
ADRENAL MEDULLA
increases the heart rate and cardiac output without signifying increasing the blood pressure and other metabolic effects; constricts vessels
Epinephrine
is in the brain and peripheral tissues, the principal transmitter substance of adrenergic neurons; dilates vessels and increases glucose release
Norepinephrine
Development of the Pineal Gland
- The pineal gland develops from the caudal part of the roof of the diencephalon.
- It appears as an epithelial thickening on the midline by the 7th week of development.
- Then, it invaginates to become a solid organ located at the roof of the mesothelium.
- Also known as EPIPHYSIS CEREBRI.
- is a slightly flattened cone shape appendage of the brain, attached to the roof of the 3rd ventricle by the peduncle.
- made up of pale staining epitheloid cells, with round or oval granular nuclei and prominent nucleoli, the PINEALOCYTES.
PINEAL GLAND
(pineal gland)
- second cell type which occur in the perivascular areas.
- less numerous and the nuclei are darker and smaller.
- neuroglial cells provide supporting network to the cells.
interstitial cells
are mulberry shaped concretions largely of hydroxyapatite, which makes the radiological landmark.
Brain sand (corpora arenacea or Psammoma’s bodies)
- The gland reaches its’ maximal development by the middle of the first decade and regresses later in life.
- It has a high level of SEROTONIN AND MELATONIN SECRETED by the pinealocytes.
- controls the onset of puberty; regulates circadian rhythms
pineal gland
- has an exocrine portion, which secretes digestive juice essential for the digestion of carbohydrates, fats and proteins, and an endocrine portion secreting hormones.
- The endocrine function is performed by a highly vascularized aggregation of secreting cells, the ISLETS OF LANGERHANS, which are scattered all throughout.
- They are over a million, but comprised only one to two per cent of the gland.
Pancreas
Development of the Islets of Langerhans
- The islets of Langerhans develops from the parenchymatous pancreatic tissue during the 3rd month of development and scattered throughout the gland.
- Insulin secretion begins on the 5th month of development
- The islets are spheroidal masses of pale staining cells arranged in a form of irregular anastomosing cords, with a few fine connective tissue fibers.
- They are more abundant in the tail of the pancreas.
- The secretion is released into the interstitium where it has access to the bloodstream.
- By special methods, there are six cell types distinguished.
Islets of Langerhans
Principal Cells of the Islets of Langerhans
- Alpha cells - Periphery, Secrete GLUCAGON ( increase blood glucose )
- Beta cells - Predominant type distributed throughout the islet comprising 60% to 90% of its mass, Secrete INSULIN (decrease blood glucose levels)
- Delta cells - Least abundant occurring anywhere in the islet, Secrete SOMATOSTATIN ( inhibit secretion of insulin,glucagon and somatotropin)
- Pancreatic polypeptide – rare, + gastric chief cells; inhibit bile secretion,pancreatic enzyme&bicarbonate secretion and intestinal motility
- is a compound tubular gland enclosed in a thick fibrous capsule, the TUNICA ALBUGINEA. Thin fibrous septa, the SEPTULA TESTIS, extend radially dividing the organ into compartments, the LOBULI TESTIS.
- Each lobule is composed of one to four highly convoluted seminiferous tubules, which constitute to the exocrine portion of the __
TESTES
Development of the Leydig Cells of Testis
- Develops from the mesenchyme between the seminiferous tubules, which are particularly abundant during the 4th to 6th months of development.
- endocrine component of the testis that are located in the interstices between the seminiferous tubules. The cells occur in groups of various sizes. Small blood vessels are usually present. The cells are LARGE AND OVOID OR POLYGONAL. They have a LARGE ECCENTRIC NUCLEUS AND GRANULAR ACIDOPHILIC CYTOPLASM, which is peripherally vacuolated. The ultrastructure typifies that of steroid secreting cells which have extensive smooth endoplasmic reticula. Peculiar to human, is a variable number of proteinaceous crystals, Reinke’s crystals.
- synthesize TESTOSTERONE
Leydig cells
- are slightly flattened, ovoid, paired organs suspended on either side of the uterus.
- has two zones; a central deeper zone, the MEDULLA, and a broad outer zone, the CORTEX.
- As the follicles increase in size, the theca folliculi differentiates into a highly vascular inner layer of secretory cells, the THECA INTERNA, which secretes ESTROGEN, and an outer layer, the theca externa, composed mainly of connective tissue.
ovaries
Development of the Theca Interna Cells of the Ovary
Develop from secondary cortical cords from the proliferation of cells in the stroma ovarii
Following ovulation, the follicular wall collapses and its granulosa cell lining is thrown into folds. There is extravasation of blood from the capillaries of the theca interna, resulting in a central clot. The theca interna and granulosa cells then enlarge and accumulate lipid and are transformed into plump, pale staining polygonal cells, the LUTEIN CELLS. This structure is now called the __
Corpus luteum
(ovary)
Two kinds of Lutein cells are distinguishable which are
- the peripheral, smaller and darker stained THECA LUTEIN CELLS, which secrete a small amount of ESTROGEN
- larger, GRANULOSA LUTEIN CELLS, which secrete PROGESTERONE
(placenta)
The syncitiotrophoblast of the chorionic villi secrete __
Human chorionic gonadotrophic hormone (HCG)
- special type of connective tissue in which fat cells predominate
- ound isolated in all loose connective tissue, but in certain places they are present in such large numbers and have such organization as to justify the designation of adipose tissue.
- are large, oval or spherical shaped cells, whose cytoplasm is displaced to the peripheral region of the cell by the presence of a single large fat droplet . The nucleus is flattened and surrounded by a small amount of cytoplasm in the periphery giving a characteristic “signet ring” appearance.
Fat
The principal functions of adipose tissue are:
- Storage of fat
- Insulation against heat loss
- Mechanical support in certain body regions
There are two types of adipose tissue, namely:
- Yellow or white adipose tissue
- Common or yellow or white adipose tissue comprise the bulk of the body fat.
- It is an adult fat or mature form of adipose tissue from which ranges in color from white to dark yellow.
- The adipose cell contains a single large fat droplet in the cytoplasm. Therefore, it is unilocular as to morphology.
This type is found in subcutaneous tissue of skin, omentum, mesenteries and retroperitoneal fat. - Brown adipose tissue
- is a fetal fat or immature form of adipose tissue
- color ranges from tan to reddish brown; cell contains multiple lipid droplets in the cytoplasm; hence, it is multilocular in morphology.
- is found in the interscapular and inguinal regions of the newborn
Endocrine function of adipose tissue
Major site for metabolism of sex steroid and glucocorticoid
(kidney)
- have a slightly basophilic cytoplasm and their specific granules are clearly demonstrated. Electron microscopy of secretory granules shows that cells are variable in shape and membrane bounded with an internal crystalline structure.
- cells secrete RENIN, which activates Angiotensinogen into Angiotensin I. Angiotensin I is inactive but is converted in the lungs to Angiotensin II, which is a potent vasoconstrictor, increasing blood pressure.
Juxta-glomerular (JG) cells
(kidney)
- Also known as polar cushion or polkissens cells. These cells are formed at one angle between the afferent and efferent arteriole at the vascular pole.
- They may produce ERYTHROPOIETIN, a hormone that stimulates erythropoiesis in the bone marrow.
Lacis cells or extraglomerular mesangial cells
- Located posterior to the sternum
- Largest in infants and children
- Produces THYMOSIN
- Matures some types of white blood cells
- Important in developing the immune system
Thymus
Pituitary Dwarfism vs Gigantism vs Acromegaly
Pituitary dwarfism - hyposecretion of growth hormone by the adenohypophysis
Gigantism - hypersecretion of growth hormone during childhood
Acromegaly - hypersecretion of growth hormone during adulthood
hyposecretion of ADH caused by damage to the neurohypophysis or the supraoptic nucleus
Diabetes insipidus
a heterogenous group of diseases, all of which lead to an elevation of blood sugar and excretion of glucose in the urine
Diabetes mellitus
Cretinism vs Myxedema vs Grave’s Disease
Cretinism = hyposecretion of thyroid hormones during the growth years. Two clinical manifestations of the cretin are dwarfism and mental retardation
Myxedema = hypothyroidism during adulthood. Hallmark of this disorder is an edema that causes the facial tissues to swell and look puffy
Grave’s disease = hyperthyroidism during adult life. This gives rise to exophthalmic goiter.
Tetany vs Osteitis fibrosa cystica
Tetany = muscle twitches or spasm and convulsions as a result of hypoparathyroidism (deficiency in calcium)
Osteitis fibrosa cystica = hyperparathyroidism that causes demineralization of bone
hypersecretion of the mineralocorticoid, aldosterone, characterized by a decrease in the body’s potassium concentration
Aldosteronism
primary adrenal insufficiency that results in hyposecretion of glucocorticoids. Clinical manifestations include lethargy, weight loss and hypoglycemia, which leads to muscular weakness
Addison’s disease
hypersecretion of glucocorticoids, especially cortisol and cortisone. Clinical manifestations include moon face, buffalo hump on the back and pendulous abdomen
Cushing’s syndrome
tumor of the chromaffin cells of the adrenal medulla, causes hypersecretion of the medullary hormones
Pheochromocytoma
The __ is formed from the incorporation of the dorsal part of the yolk sac into the embryo due to the craniocaudal folding and lateral folding of the embryo.
primitive gut tube
The primitive gut tube extends from the oropharyngeal membrane to the cloacal membrane and is divided into the __
foregut, midgut, and hindgut
Histologically, the general plan of the adult gastrointestinal tract consists of a __
- mucosa (epithelial lining and glands, lamina propria, and muscularis mucosal)
- submucosa
- muscular externa
- adventitia or serosa.
Embryologically, the epithelial lining and glands of the mucosa are derived from __, whereas the other components are derived from visceral mesoderm.
endoderm
- derivatives are supplied by the celiac trunk except esophagus
- lies caudal to the pharyngeal tube and extends as far caudally as the liver outgrowth
- extends from the esophagus down to the second part of the duodenum where the common bile duct enters the GI tract
- consists of esophagus, stomach, liver, gallbladder, pancreas, proximal duodenum, trachea, oropharynx and salivary gland
Foregut
- The middle part remains temporally connected to the yolk sac by means of the vitelline duct, or yolk stalk
- extends to the junction of the middle and distal thirds of the transverse colon (known as CANNON’S POINT)
- begins caudal to the liver bud and extends to the junction
- supplied by the superior mesenteric artery
- consists of lower duodenum, jejunum, ileum, cecum, appendix, ascending colon and proximal 2/3 of the transverse colon
midgut
- extends from the left third of the transverse colon to the
cloacal membrane - supplied by the inferior mesenteric artery
- consists of Distal 1/3 of the transverse colon, descending colon, sigmoid colon, rectum, and upper anal canal
hindgut
- occurs when the tracheoesophageal septum deviates too far dorsally, causing the esophagus to end as a closed tube. - About 33% of patients with __ also have other congenital defects associated with the VATER (vertebral defects, anal atresia, tracheoesophageal fistula, and renal defects) or VACTERL (similar to VATER plus cardiovascular defects and
upper limb defects) syndromes - It is associated clinically with polyhydramnios (the fetus is unable to swallow amniotic fluid) and a tracheoesophageal fistula
- esophagus terminates blindly in a blunted esophageal pouch. There is a distal esophageal connection with the trachea at the carina
Esophageal atresia
- occurs when the lumen of the esophagus is narrowed and usually involves the midesophagus.
- may be caused by submucosal/muscularis externa hypertrophy, remnants of the tracheal cartilaginous
ring within the wall of the esophagus, a membranous diaphragm obstructing the lumen probably due to incomplete recanalization.
Esophageal stenosis
- occurs when abdominal contents herniates through the
umbilical ring and persists outside the body, covered variably by a translucent peritoneal membrane sac (a light gray, shiny sac) protruding from the base of the umbilical cord. - Large __ may contain stomach, liver, and intestines. Small __ contain only intestines.
Omphalocele
- occurs when there is a defect in the ventral abdominal wall, usually to the right of the umbilical ring, through which there is a massive evisceration of intestines (other organs may also be involved). The intestines arenot covered by a peritoneal membrane, are directly exposed to amniotic fluid, are thickened, and are covered with adhesions.
Gastroschisis
- occurs when the anal membrane fails to perforate; a layer of tissue separates the anal canal from the exterior.
Imperforate anus
- occurs when the anal canal ends as a blind sac below the puborectalis muscle due to abnormal formation of the urorectal septum.
- It is usually associated with rectovesical, rectourethral, or rectovaginal fistula.
Anal agenesis
- occurs when the rectum ends as a blind sac above the puborectalis muscle due to abnormal formation of the urorectal septum.
- It is the most common type of anorectal malformation and is usually associated with a rectovesical, rectourethral, or
rectovaginal fistula
Anorectal agenesis
- occurs when both the rectum and anal canal are present but remain unconnected due to either abnormal recanalization or a compromised blood supply causing focal atresia.
Rectal atresia