WEEK 4: Embryology Anatomy and histology of the adrenals

Question 1

Describe blood supply to the adrenal gland.

Answer 1

Arteries:
The arteries supplying each gland are three in number:

*Superior suprarenal arteries
*Middle suprarenal arteries
*inferior suprarenal arteries arise

Question 2

Describe venous drainage of the adrenal gland.

Answer 2

Veins: A single vein emerges from the hilum of each gland and drains into the
inferior vena cava on the right and
left renal vein on the left.

Question 3

Describe nerve supply to the adrenal gland.

Answer 3

Nerve Supply:
*Preganglionic sympathetic fibers derived from the splanchnic nerves supply the glands.

*Most of the nerves end in the medulla of the gland.

Question 4

Describe lymphatic drainage of the adrenal gland.

Answer 4

Lymph Drainage:
The lymph drains into the lateral aortic nodes

Question 5

Embryology of the Suprarenal Glands.
Q: From which embryonic origin does the adrenal cortex develop?

Q: From which cells does the adrenal medulla develop?

Answer 5

The two parts of the adrenal gland develop from different origins.

1. Cortex develops from the celomic epithelium (mesothelium) derived from mesoderm
2. Medulla develops from the neural crest cells

Question 6

Describe the embryology of the adrenal cortex

Answer 6

Step 1: Formation of the Intermediate Mesoderm

The intermediate mesoderm forms during early embryogenesis alongside the neural tube and somites.
Step 2: Development of the Urogenital Ridge

The intermediate mesoderm gives rise to the urogenital ridge, which will later differentiate into the adrenal cortex and parts of the urinary and reproductive systems.
Step 3: Formation of the Celomic Epithelium

The celomic epithelium (mesothelium) forms on the surface of the urogenital ridge. This epithelium is derived from the mesoderm.
Step 4: Differentiation into Adrenal Cortex

The cells of the celomic epithelium proliferate and differentiate to form the adrenal cortex. This involves the migration and condensation of these cells.
Step 5: Layer Formation

The adrenal cortex differentiates into three distinct layers: the zona glomerulosa, zona fasciculata, and zona reticularis. These layers develop in a sequential manner and each produces different hormones.
Step 6: Functional Maturation

As the fetal adrenal cortex develops, it begins to produce steroid hormones. Functional maturation continues after birth, with the adrenal cortex fully developing into its adult structure.

Question 7

Discuss the embryology of the adrenal medulla.

Answer 7

Step 1: Formation of Neural Crest Cells

Neural crest cells are a group of cells that emerge from the dorsal aspect of the neural tube during early embryonic development. These cells are highly migratory and pluripotent.
Step 2: Migration of Neural Crest Cells

Neural crest cells migrate from the neural tube to various parts of the developing embryo. A subset of these cells migrates to the region where the adrenal glands will form.
Step 3: Aggregation at the Future Adrenal Gland Site

The migrating neural crest cells aggregate near the developing adrenal cortex, which is derived from the mesodermal celomic epithelium.
Step 4: Differentiation into Chromaffin Cells

Once at the site, these neural crest cells differentiate into chromaffin cells under the influence of local signaling molecules and the developing adrenal cortex. Chromaffin cells are the main cell type found in the adrenal medulla.

Step 5: Formation of the Adrenal Medulla

The chromaffin cells cluster together to form the adrenal medulla, which becomes encapsulated by the developing adrenal cortex.
Step 6: Functional Maturation

The adrenal medulla continues to mature and eventually begins to produce catecholamines, including adrenaline (epinephrine) and noradrenaline (norepinephrine), which are essential for the body’s fight-or-flight response.
Step 7: Integration with the Sympathetic Nervous System

The adrenal medulla functions as part of the sympathetic nervous system. The chromaffin cells receive direct input from preganglionic sympathetic fibers, allowing for rapid hormone release in response to stress.

Question 8

Q: During which week of development does the coelomic epithelium medial to the developing gonadal ridge proliferate?

Q: Where does the coelomic epithelium proliferate during the 6th week of development?

Answer 8

A: During the 6th week of development.

A: Medial to the developing gonadal ridge, between the mesenteric root and the gonadal primordium.

Question 9

Q: What happens to the newly formed cells from the coelomic epithelium during adrenal cortex development?

Q: What happens during the second wave of cell migration in adrenal cortex development?

Q: What surrounds the fetal cortex during adrenal development?

Answer 9

A: The newly formed cells get separated from the surface epithelium, enter the underlying mesoderm, and form the fetal cortex.

A: A second wave of delaminating cells migrates and forms a thinner definitive (permanent) cortex surrounding the fetal cortex.

A: The thinner definitive (permanent) cortex formed by the second wave of delaminating cells.

Question 10

Q: From which cells is the adrenal medulla formed?

Q: When do the sympathochromaffin cells invade the cortex during development?

Answer 10

A: The adrenal medulla is formed from the sympathochromaffin cells of the neural crest.

A: From Day 45 of gestation.

Question 11

Q: How developed is the adrenal medulla at birth?

Q: What proportion of the glandular parenchyma does the definitive cortex make up at birth?

Answer 11

A: The adrenal medulla is only slightly developed and is not yet functional at birth.

A: The definitive cortex makes up only 15-20% of the glandular parenchyma.

Question 12

Q: Which nerve fibers grow into the adrenal medulla, and what do they release?

Q: How do preganglionic sympathetic nerve fibers influence the medullary cells?

Answer 12

A: Preganglionic sympathetic nerve fibers grow into the adrenal medulla and release epinephrine and norepinephrine upon sympathetic stimulation.

A: They influence the activity of the medullary cells by releasing epinephrine and norepinephrine.

Question 13

Compare Fetus Vs Adult Suprarenal gland.

Answer 13

The fetal adrenal gland is relatively large compared to the adult gland. At birth, the adrenal gland is roughly the same size as the kidney.
The fetal gland is about 10-20 times larger relative to body weight than the adult adrenal gland.

Question 14

Why is the fetal adrenal gland larger than the adult one?

Answer 14

1. Hormone Production for Pregnancy:

The large fetal zone of the adrenal cortex produces significant amounts of DHEA-S, which the placenta converts to estrogens. These estrogens are crucial for maintaining pregnancy and supporting fetal development.

2. Rapid Growth and Development:

The adrenal gland grows rapidly during fetal development to meet the high demands for steroid hormones, which are important for various developmental processes, including lung maturation and regulation of electrolyte balance.

3. Preparation for Postnatal Life:
   Although the medulla is not fully functional at birth, the large size of the fetal adrenal gland ensures that it has sufficient capacity to support the initial needs of the newborn immediately after birth.

Question 15

Discuss the histology of the adrenal gland.

Answer 15

Encased in a connective tissue capsule that

Extends septae into the substance of the gland.
partitioned into cortex and medulla.

*The medulla is fairly homogeneous,

3 concentric zones can be distinguished in the cortex:
zona glomerulosa - thin, outermost zone

Question 16

Discuss the Differences in the cortical cords

Answer 16

Names reflect cord arrangements
Z. glomerulosa – knotted
Z. fascicula – straight cords
Z.reticularis – interconnected cords

Question 17

Discuss the adrenal medulla histology.

Answer 17

Cells loosely organized into clusters and cords.

Proper sympathetic ganglion nerve cells can occasionally be found in the medulla.

Question 18

Describe cortical and medullary blood supply.

Answer 18

1. The adrenal gland receives blood from three main arteries: the superior suprarenal artery, the middle suprarenal artery, and the inferior suprarenal artery.
2. Blood enters the adrenal cortex through capsular arteries, which branch into cortical arterioles. These arterioles form a network of capillaries and sinusoids that supply the cortex.
3. Blood flows through the cortical capillaries and sinusoids, supplying the zona glomerulosa, zona fasciculata, and zona reticularis.
4. Blood from the cortical capillaries and sinusoids drains into medullary arterioles, which then supply the adrenal medulla.
5. Medullary arterioles provide blood to the adrenal medulla, allowing it to receive oxygenated blood and regulatory hormones produced by the cortex.
6. The adrenal medulla has a dual blood supply: one from the medullary arterioles (derived from cortical blood) and another from direct medullary arteries.
7. The dual blood supply ensures that the medulla receives both oxygenated blood and hormones from the cortex, facilitating efficient catecholamine production and release.
8. Blood exits the adrenal gland through central medullary veins, which drain into the adrenal veins and subsequently into the inferior vena cava or renal vein.