Histology - Endocrine System Ii: Thyroid, Parathyroid, Adrenals

Front 1

Thyroid Structure and General Info

Back 1

Consists of two main lobes, looks kind of like a giant capital letter H

It is the only gland known to store hormones extracellularly. Otherwise, they are normally stored in secretory vesicles or cholesterol in the case of steroid hormones

Front 2

Thyroid Follicle - epithelium and structure; surrounding cells and function

Back 2

Epithelium - simple cuboidal
It is a ball of cells
There is a BM and the lumen is called the colloid, which is stained liquid

In between the follicles are cells called the Parafollicular cells, which secrete calcitonin

Front 3

Thyroid Gland Makes 2 Hormones:

Back 3

1) Thryroid Hormone - T3 and T4

2) Calcitonin - involved in calcium regulation

Front 4

T3 and T4

Back 4

Regulate basal metabolic rate (BMR) in mammals. T3 and T4 serve different functions in other animals. BMR is the amount of energy expended while at rest in a neutrally temperate environment.

Front 5

Colloid

Back 5

It is a chain of amino acids (proteins) otherwise known as Thyroglobin. Some of these amino acids are Tyrosine, which are bonded to other Tyrosines via peptide bonds.

Front 6

Formation of T3 and T4 (Part I)

Back 6

From a blood vessel located outside of the thyroid follicle, amino acids are released into its epithelium. These go through the follicle's rough endoplasmic reticulum, then to the Golgi, and then into the colloid. From the same blood vessel, I- is released into the epithelium, which is then oxidized into I, and then sent into the colloid.

Front 7

Formation of T3 and T4 (Part II)

Back 7

Some of the colloid is picked up and transferred into the epithelium, where lysozymes break it down into T-T, surrounded by I's. This molecule then exits the follicle, and one of the I's can go back to the blood vessel, only to be put back into the system again.

The T3 and T4 are the active products, they interact with the receptors located inside the cell

Front 8

Formation of T-doublets

Back 8

The side branch of the amino acid is removed of tyrosine (not the peptide bond). An ether bond is made for part of the tyrosine to link with another whole tyrosine, forming a T-doublet. The iodines link to the T, and in the end, the thryoglobin has part of 1 T attached to another T, with 1-4 I's bonded to it

Front 9

Another role of T3 and T4

Back 9

TSH comes from the pituitary gland and stimulates the thyroid gland, which makes T3 and T4. If too much of this hormone is produced, then T3 and T4 can provide a negative feedback mechanism in which the pituitary gland shuts down so that things can reach equilibrium again.

Front 10

If there is a lack of iodine in one's diet (if salt deposits lack iodine)

Back 10

Then T-doublets will not have enough I to function, meaning T3 and T4 will not function, but will still form. A lot of TSH will be produced so that the thyroid will be hyperstimulated, which will cause more mitosis in the thyroid gland, leading to an enlarged thyroid gland called a Goiter.

Front 11

Parathyroid Glands

Back 11

They are 4 little glands embedded within the thyroid gland

Front 12

Parathyroid Glands produce 2 cell types

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1) Principal Cells (or chief cells) - make and secrete parathyroid hormone. These cells don't really look like anything, are purple, need the next cell type to be able to differentiate between the two and find them.

2)Oxyphil Cells - No main function has been found but they help identify principal cells. Oxyphil cells are a bit more dispersed, and are usually located in the middle surrounded by principal cells. They are eosinophilic, so their cytoplasm is stained pink, which is the dead giveaway.

*Adipose tissue surrounds these cells.

Front 13

If there is a decrease in blood calcium...

(target cells of the hormone)

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Then there is an increased release of parathyroid hormone, and thus blood calcium shoots up.

Parathyroid hormone therefore can target bone (osteocytes have a quicker response to it than osteoclasts), kidneys (increased reabsorption of Ca++), and intestines (enterocytes increase Ca++ absorption from food)

Front 14

If there is an increase in blood calcium levels...

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Then there is an increase in calcitonin release, which decreases osteoclast activity, which then slowly decreases Ca++.

Front 15

Parathyroid hormone vs. Calcitonin

Back 15

Parathyroid hormone is our main Ca++ regulator. We could not live without it. But we could live without calcitonin b/c it's slow in Ca++ regulation.

Front 16

Adrenals Structure

Back 16

Contain an outer CT capsule, a cortex, and a medulla (most inner region).

Front 17

Compared to the Sympathetic Nervous System

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They are an addendum to the sympathetic nervous system.

However, the neuron secretions go straight into the blood stream, found in the cortex

Front 18

Medulla

Back 18

Produces Adrenaline and Noradrenaline (AKA epinephrine and norepinephrine), which are involved in the fight or flight response in the sympathetic nervous system.

Noradrenaline is used to make the adrenaline. These 2 different hormones generally have the same effect, but a bit different on different receptors.

Front 19

Adrenal Cortex

Back 19

It has three zones in which the cells are arranged in different patterns respectively.

1) Next to the CT capsule, the first zone is the Zone Glomerulosa, in which there is a round pattern of cells. The steroid aldosterone is made here, which regulates sodium and potassium balance in the blood.

2) Next to that is the Zona Fasciculata, which are cells in a straight shape. They make the steroid cortisol, which is involved in the response to stress; it increases blood pressure, blood sugar levels, may cause infertility in women, and suppresses the immune system.

3.) The next zone is the Zone Reticularis, which looks like a network of cells and are also more dense than the previous cells. They also make cortisol, although it is mainly made by the previous zone. This zone also makes the steroid androgen, which is found in both sexes, and is the general term for any male hormone. The major androgen is testosterone. It is also the precursor for all estrogens

*ACTH affects the first 2 zones, but not the 3rd zone.
*After this zone is the medulla.