Anatomy of the Hypophysis

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Questions and Answers

What is the percentage of the mass of hypophysis accounted for by the pars distalis?

90%

100%

75% (correct)

50%

Which type of cells in the pars distalis produce two hormones?

Chromophobes

Acidophils

Gonadotropic cells (correct)

Basophils

What is the function of the superior hypophyseal arteries?

Supply the neural stalk (correct)

Drain the hypophyseal portal system

Supply the neurohypophysis

Supply the adenohypophysis

What is the term for the capillary plexus that irrigates the neural stalk?

Fenestrated capillary plexus Signup and view all the answers

What is the function of the hypophyseal portal system?

Carry neurohormones from the neural stalk to the adenohypophysis Signup and view all the answers

What is the origin of the adenohypophysis?

Oral ectoderm Signup and view all the answers

What type of cells are interspersed with capillaries in the pars distalis?

Epithelial cells Signup and view all the answers

What is the mechanism by which hormones secreted by endocrine cells control the release of peptides from the neural stalk and the pars distalis?

Direct effect Signup and view all the answers

What is the primary function of inhibin and activin produced in the gonads?

To inhibit the secretion of FSH Signup and view all the answers

Which of the following is NOT a function of the pars tuberalis?

Producing MSH Signup and view all the answers

What is the main component of the neurohypophysis?

Unmyelinated axons of secretory neurons Signup and view all the answers

What is the function of Hering's bodies in the neurohypophysis?

Storing neurosecretory granules Signup and view all the answers

What is the primary source of oxytocin in the body?

Neurohypophysis Signup and view all the answers

What is the primary stimulus for the release of ADH?

Increased tonicity of the blood Signup and view all the answers

What is the main effect of ADH on the kidney?

Increased permeability of collecting tubules to water Signup and view all the answers

What is the function of pituicytes in the neurohypophysis?

Supporting the axons of secretory neurons Signup and view all the answers

What is the function of oxytocin in the mammary glands?

Stimulation of myoepithelial cell contraction Signup and view all the answers

Which of the following is NOT a characteristic of secretory neurons in the neurohypophysis?

Having myelinated axons Signup and view all the answers

What is the primary function of dopamine produced in the central nervous system?

Inhibiting the secretion of prolactin Signup and view all the answers

What triggers the secretion of oxytocin during childbirth?

Distension of the uterine cervix Signup and view all the answers

What is the shape of the adrenal glands?

Half-moon shaped Signup and view all the answers

What is the origin of the adrenal cortex?

Coelomic epithelium Signup and view all the answers

What is the function of the cortical arteries in the adrenal glands?

Form an extensive capillary network in the medulla Signup and view all the answers

What is the approximate weight of both adrenal glands together?

8gm Signup and view all the answers

What type of molecules are steroid hormones?

Lipid soluble Signup and view all the answers

Which layer of the adrenal cortex is characterized by columnar cells arranged in closely packed rounded or arched cords?

Zona glomerulosa Signup and view all the answers

What is the name of the cells in the zona fasciculata due to the presence of lipid droplets in their cytoplasm?

Spongiocytes Signup and view all the answers

What is the arrangement of cells in the zona fasciculata?

One or two thick straight cords Signup and view all the answers

Which layer of the adrenal cortex lies between the zona fasciculata and the medulla?

Zona reticularis Signup and view all the answers

What is characteristic of the cells in the zona reticularis?

Presence of large and numerous lipofuscin pigment granules Signup and view all the answers

What is the purpose of the medullary veins?

To drain the blood from the adrenal medulla Signup and view all the answers

Where does the blood from the medullary arteries originate from?

From the capillaries of the cortex Signup and view all the answers

Where is cholesterol converted to the final adrenal steroids?

Partly in the mitochondria and partly in the SER Signup and view all the answers

Which of the following hormones promotes protein and lipid degradation?

Cortisol Signup and view all the answers

What is the main function of mineralocorticoids in the distal tubules?

Stimulating the reabsorption of sodium Signup and view all the answers

What is the origin of the cells of the adrenal medulla?

Neural crest Signup and view all the answers

What is the function of chromogranin in the secretory granules of the adrenal medulla?

Binding protein for catecholamines Signup and view all the answers

What is the main effect of glucocorticoids on the immune response?

Suppressing the immune response Signup and view all the answers

What is the fate of DHEA in several tissues?

It is converted to testosterone Signup and view all the answers

What is the characteristic of the cells of the adrenal medulla?

They have lost their axons and dendrites during embryonic development Signup and view all the answers

Study Notes

Hypophysis (Pituitary Gland)

Develops from oral ectoderm and is subdivided into three portions: pars distalis (anterior lobe), pars tuberalis, and pars intermedia
Blood supply:
- Superior hypophyseal arteries supply the neural stalk from above
- Inferior hypophyseal arteries supply the neurohypophysis from below
- Hypophyseal portal system carries neurohormones from the neural stalk to the adenohypophysis

Adenohypophysis

Pars distalis:
- Composed of cords of epithelial cells interspersed with capillaries
- Hormones produced by these cells are stored as secretory granules
- Accounts for 75% of the mass of the hypophysis
- Cells can be recognized as chromophobes, basophils, and acidophils based on staining
- Basophils and acidophils are named for the hormones they produce (e.g., gonadotropic cells produce two hormones)
Control of the pars distalis:
- Cells are controlled by peptide hormones produced in the hypothalamic aggregates of neurosecretory cells and stored in the neural stalk
- Hormones are transported to the pars distalis through the capillary plexus
- Additional control mechanisms include:
  - Direct effect of hormones secreted by endocrine cells on the release of peptides from the neural stalk and the pars distalis
  - Action of nerve impulses or molecules produced neither in the hypothalamic nuclei nor in the target tissue (e.g., inhibin and activin produced in the gonads, dopamine produced in the central nervous system)

Pars Tuberalis

Funnel-shaped region surrounding the infundibulum of the neurohypophysis
Most cells secrete gonadotropins (FSH and LH)

Pars Intermedia

Develops from the dorsal portions of Rathke's pouch
Rudimentary region made up of cords and follicles
Probably produces MSH (Melanocyte Stimulating Hormone)

Neurohypophysis

Consists of the pars nervosa and the neural stalk
Composed of unmyelinated axons of secretory neurons situated in the supraoptic and paraventricular nuclei
Secretory neurons have well-developed Nissl bodies related to the production of neurosecretory material
Neurosecretions are transported along the axons and accumulate at their nerve endings to form Hering's bodies
Hering's bodies contain neurosecretory granules which are released and enter the fenestrated capillaries
Neurosecretory materials consist of two hormones: Anti-diuretic hormone (vasopressin) and oxytocin

Cells of the Neurohypophysis

Consists mainly of axons from hypothalamic neurons
About 25% of its volume consists of a specific type of highly branched glial cells called pituicytes

Actions of the Hormones of the Neurohypophysis

ADH (vasopressin):
- Released in response to increased tonicity of the blood
- Main effect is to increase the permeability of collecting tubules of the kidney to water, leading to reabsorption of water and regulation of osmotic balance
Oxytocin:
- Stimulates contraction of the myoepithelial cells that surround the alveoli and ducts of the mammary glands during nursing and of the smooth muscle of the uterine wall during copulation and childbirth
- Secretion of oxytocin is stimulated by nursing or by distension of the vagina or the uterine cervix

Adrenal (Suprarenal) Gland

Paired organs that lie near the superior poles of the kidneys
Consists of two concentric layers: a yellow peripheral layer, the adrenal cortex, and a reddish-brown central layer, the adrenal medulla
Adrenal cortex and medulla can be considered two organs with distinct origins, functions, and morphological characteristics

Blood Supply of the Adrenal Gland

Supplied by several arteries that are divided into three groups: arteries that irrigate the capsule, cortical arteries, and medullary arteries
Medullary arteries pass through the cortex and form an extensive capillary network in the medulla
Cells in the medulla are bathed with both arterial blood from the medullary arteries and venous blood originating from the capillaries of the cortex

Adrenal Cortex

Cells have the typical ultrastructure of steroid-secreting cells
Synthesize and secrete steroid hormones upon demand
Steroids are lipid-soluble molecules that diffuse through the plasma membrane and do not require the specialized process of exocytosis for their release
Can be subdivided into three concentric layers: zona glomerulosa, zona fasciculata, and zona reticularis

Cortical Hormones and Their Action

Adrenal steroids originate from cholesterol
Converted to final hormones partly in the mitochondria and partly in the SER
Secreted steroids can be divided into three groups: mineralocorticoids (aldesterone), glucocorticoids (cortisol), and androgens (DHEA)
Mineralocorticoids act mainly on the distal tubules and stimulate the reabsorption of sodium by epithelial cells
Glucocorticoids affect the metabolism of carbohydrates, promote protein and lipid degradation, and suppress the immune response
DHEA is a weak androgen that exerts its action after being converted into testosterone in several tissues

Adrenal Medulla

Composed of polyhedral cells arranged in cords or clumps and supported by reticular fiber network
Profuse capillary supply intervenes between adjacent cords
Cells arise from the neural crest as do the postganglionic neurons of sympathetic and parasympathetic ganglia
Cells of the adrenal medulla can be considered modified sympathetic postganglionic neurons that have lost their axons and dendrites during embryonic development and become secretory cells
Secretory granules contain one or the other type of catecholamine, epinephrine or norepinephrin

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Description

Learn about the different parts and blood supply of the hypophysis, including the adenohypophysis and neurohypophysis.