Thymus and Endocrine Glands of the Abdomen and Pelvis

Question 1

Thymus
(a) location
(b) histological features
(c) cell types
(d) secretions

Answer 1

(a) anterior and superior mediastinum
(b) Each lobe of the gland is surrounded by a dense capsule of connective tissue and divided internally into incomplete lobules by connective tissue septae. Each lobule has a highly cellular basophilic cortex and a light staining medulla. The medulla contains Hassall’s corpuscles, which are regressed epithelial cells.
(c) thymocytes, epithelioreticular cells, macrophages and dendritic cells
(d) thymosin, thymulin, thymopoietin - secreted by the epithelioreticular cells.
[Slide 1] [Slide 2: Hassall’s corpuscles]

Question 2

The adrenal gland is located on the upper pole of each kidney. Each gland comprises of an outer cortex and an inner medulla. Outline the histological layers of the adrenal cortex and state their secretions and the functions of their secretions.

Answer 2

1. Zona glomerulosa [glomerular-like clusters of cells]: mineralocorticoids, mainly aldosterone. This region is stimulated by angiotensin II. Aldosterone targets the distal convoluted tubule of the kidneys where it promotes Na+ and water reabsorption as well as K+ secretion. Through this mechanism, it regulates blood pressure and electrolyte balance.
2. Zona fasciculata [two-cell wide vertical cords]: glucocorticoids, mainly cortisol [the zona fasciulata secrets a basal level of cortisol but can produce bursts of the hormone in response to Adrenocorticotropic Hormone (ACTH) from the anterior pituitary]. Cortisol functions: 1. induces stress response, 2. metabolism regulation [stimulates gluconeogenesis], 3. Inflammation suppression, 4. Blood pressure regulation
3. Zona reticularis [one-cell wide anastomosing rows]: androgens, mainly dehydroepiandosterone, dehydroepiandosterone sulfate and androstenedione [the production of these hormones is also stimulated by ACTH]
4. [Slide] [Virtual Microscope 1] [Virtual Microscope 2]

Question 3

Discuss the cell types, secretions and stimulation of the adrenal medulla.

Answer 3

Cell types:
chromaffin cells

Secretions:
circulating catecholamines: adrenaline (epinephrine), noradrenaline (norepinephrine), derived from tyrosine. These hormones are responsible for the fight or flight response.

Stimulation:
The adrenal medulla receives input from the sympathetic nervous system through preganglionic nerve fibres originating from the thoracic spinal cord from T5 to T11. Additionally, cortisol promotes epinephrine synthesis in the medulla.

[Virtual Microscope 1] [Virtual Microscope 2]

Question 4

The pancreas
(a) location
(b) gross parts
(c) histological parts

Answer 4

(a) the stomach bed, around the duodenal curve
(b) tail, body, neck, head and uncinate process
(c) exocrine and endocrine components

Question 5

The endocrine pancreas consists of scattered cells called ____(a)____ which are well vascularized. They are found all over the pancreas but are especially abundant in the ____(b)____.

Answer 5

(a) islets of Langerhans
(b) tail

[Virtual Microscope 1] [Virtual Microscope 2]

Question 6

Name the cell types, secretions and physiological effects of the secretions of the endocrine pancreas.

Answer 6

(a) Alpha cells (A-cells); produce glucagon which elevates sugar glucose levels.
(b) Beta cells (B-cells); produce insulin which lowers blood sugar levels.
(c) Delta cells (D-cells); produce somatostatin which inhibits pancreatic secretions
(d) PP cells (F-cells); produces pancreatic polpeptide which slows down food absorption

Question 7

The Endocrine Testis
The capsule of the testis is known as the ____(a)____. The testicular parenchyma consists of seminiferous tubules and intersitital tissue.
Present within the seminiferous epithelium are Sertoli cells which produce: ____(b)____ [5 secretions].
The interstitial cells of Leydig produce ____(c)____ [2 secretions].

Answer 7

(a) tunica albuginea
(b) Androgen Binding Protein (ABP), inhibin, Mullerian-inhibiting Factor (MIF), Stem Cell Factor (SCF), glial cell-line derived neurotrophic factor (GDNF)
(c) testosterone, dihydrotestosterone

[Slide 1] [Slide 2]
[Virtual microscope 1 ] [Virtual microscope 2]

Further notes:
Androgen Binding Protein (ABP): this is a glycoprotein that binds to androgens and estrogens. When produced by the Sertoli cells in the seminiferous tubules of the testis, it is called androgen-binding protein. ABP concentrates testosterone in the luminal compartment of the seminiferous tubule, where high concentrations of testosterone are essential for normal maturation of the developing sperm.

Inhibin: Inhibin is a hormone secreted by the Sertoli cells that acts primarily to inhibit the secretion of follicle-stimulating hormone (FSH) by the anterior pituitary gland.

Mullerian-inhibiting factor: It inhibits the development of the female reproductive tract in the male embryo. Therefore, MIF is critical to sex differentiation at a specific time during fetal development.

Question 8

What are the functions of androgens?

Answer 8

1. In the embryo, secretion of testosterone and other androgens is essential for the normal development of the gonads and other male genital organs in the male fetus.
2. At puberty, secretion of testosterone is responsible for the initiation of sperm production, accessory sex gland secretion and development of secondary sexual characterisitcs.
3. In the adult, secretion of testosterone is essential for the maintenance of spermatogenesis and of secondary sex characteristics, genital ducts, and accessory sex glands.
4. Androgens are responsible for influencing male libido.
5. Androgens are important in the maintenance and enhancement of bone and muscle mass in males.

Question 9

The Endocrine Ovary
Histologically, the ovary contains a cortex and a medulla. The cortex contains follicles at various stages of maturation. Name the cell types found in:
(a) a mature ovarian follicle
(b) the corpus luteum

Answer 9

(a) granulosa cells, theca interna cells
(b) granulosa lutein cells, theca lutein cells
(c) [Slide 1
(d) [Virtual Microscope 1] [Virtual Microscope 2]

Question 10

State three effects of ovarian hormones.

Answer 10

1. They promote growth and maturation of internal and external sex organs.
2. They are responsible for the female sex characteristics that develop at puberty.
3. They act on mammary glands to promote breast development by stimulating ductal and stromal growth and accumulation of adipose tissue.

Question 11

_________(a)__________ hormone stimulates theca ____(b)_____ cells to secrete ______(c)_____. ____________(d)_________ hormone stimulates the follicular/granulosa cells to convert _____(c)______ to _____(e)______.

Answer 11

(a) Luteinising
(b) interna
(c) androgens
(d) Follicle stimulating
(e) estrogen