Endocrinology: Overview of Endocrine Systems

Question 1

Way to split endocrine glands (by location)

Answer 1

Central and peripheral endocrine glands

Question 2

Where are central endocrine glands?

Answer 2

In the brain

Question 3

Examples of central endocrine glands

Answer 3

In the brain
- Pineal
- Hypothalamus*
- Posterior and anterior pituitary*

Question 4

What are peripheral endocrine glands?

Answer 4

All other endocrine glands, i.e., those not in the brain

Question 5

Examples of peripheral endocrine glands

Answer 5

Endocrine glands not in the brain
- Thyroid*
- Parathyroid*
- Thymus
- Pancreas
- Adrenal*
-Kidney
- Testes/ ovaries

• = vital glands

Question 6

Role of hypothalamus

Answer 6

important integration of endocrine and nervous systems; efferent signals bring about changes that help to re-establish normal values

Question 7

Role of posterior and anterior pituitary glands and hypothalamus, in homeostasis

Answer 7

Maintain critical roles in maintaining homeostasis (endocrine = chemical signals, work with nervous system = electrical signals)
Hypothalamus = linkage between endocrine and nervous system

Question 8

How do the endocrine and nervous systems work together? Why is this important?

Answer 8

The endocrine system works alongside the nervous system (integrated control systems)
Nervous system acts via electrical signals to control rapid responses of the body
Endocrine system acts via hormones secreted into blood to control activities that require duration rather than speed (chemical signals)
Integrated control systems essential for survival of body cells, and hence systems to work together to achieve body homeostasis

Question 9

Endocrine cells

Answer 9

Secrete hormones into the blood stream that carries them to target cells often distant from the endocrine cells

Question 10

Where are endocrine cells found?

Answer 10

Single scattered cells, e..g, enteroendocrine cells in epithelium lining of GIT
Clumped together into glands e.g., adrenal glands

Question 11

What do target cells for hormones have?

Answer 11

Appropriate receptors for endocrine signals, making them specific

Question 12

Hormones

Answer 12

Released from endocrine cells
Chemical messengers
Regulate activity of target cells

Question 13

Neurohormones

Answer 13

Substances secreted by specialised neurons (neurosecretory/ neuroendocrine cells, rather than glandular epithelial cells) into the bloodstream
Can also serve as a neurotransmitter or as an autocrine/ paracrine messenger
Meet definition of a hormone (enter bloodstream, act on target cells

Question 14

Example of a neurohormone

Answer 14

ADH, catecholamines from the adrenal medulla (adrenal cells are essentially modified neurons

Question 15

Paracrine secretions

Answer 15

Influence activity of adjacent cells
E.g., mast cells (paracrine cell) release histamine which act on nearby blood vessels to increase vasodilation and permeability

Question 16

Autocrine secretions

Answer 16

Influence the activity of self-cells (act locally, generally don’t enter bloodstream)

Question 17

Main types of hormones

Answer 17

• Proteins and glycoproteins
• Small peptides
• Amino acid derivatives, including amines
• Steroids

Question 18

E.g., of proteins and glycoproteins hormones

Answer 18

Growth hormone, insulin

Question 19

E.g., of small peptide hormones

Answer 19

Thyroid stimulating hormone (TSH), oxytocin

Question 20

E.g., of amino acid derivative hormones

Answer 20

Adrenaline, thyroxine

Question 21

E.g., of steroid hormones

Answer 21

Cortisol, testosterone, progesterone

Question 22

Three broad types of hormones. How do these differ?

Answer 22

proteins, amines and steroids

differ in way they’re synthesised, transported, stored, released and regulated

Question 23

Actions of water-soluble (hydrophilic) hormones

Answer 23

• Peptides and most amine hormones are hydrophilic = lipophobic, hence cannot pass through lipid bilayer of cell membrane
• Hormone binds to receptor in cell membrane
• Binding activates 2nd messengers, e.g., cAMP
• Second messengers in turn activate enzymes that produce a specific physiological response
• Act primarily at a translational level
• Calcium ions serve as important messengers within cells

Question 24

Actions of fat soluble (lipophilic) hormones

Answer 24

• Steroid hormones and the thyroid hormones are hydrophobic = lipophilic
• Receptor is in the cytoplasm or nucleus, as they can pass through the cell membrane
• Acts at transcription level
• Steroid hormones are generally slower in triggering physiological changes in their target cells compared with non-steroid hormones

Question 25

How does a typical endocrine gland develop?

Answer 25

• Ingrowth of cord of cells from surface epithelial cells during development
• Attachment to surface lost
• Cells release secretion into capillaries

Question 26

General structure of endocrine glands

Answer 26

• Clumps and strands of cells
• Supported by reticular fibres and minimal CT cells
• Minimal barriers between cells releasing their secretions and adjacent capillaries
• Fenestrated capillaries and sinusoids (gaps and spaces) to facilitate diffusion of hormones into bloodstream
• No duct system

Question 27

Features of typical amine, polypeptide, protein and glycoprotein hormone producing cells

Answer 27

• Secrete water soluble (lipophobic) hormones
• Have many small membrane-bound secretory granules (where the hormones are stored)
• Polarity is not as obvious as exocrine cells (no significant difference in structure between the top and bottom of the cell)
• Contain small to moderate amounts of RER and Golgi (typically don’t secrete large volume of hormone

Question 28

Features of typical steroid hormone producing cells

Answer 28

• cholesterol stored in lipid droplets (often identifiable under the microscope)
• cholesterol converted to steroid hormone in SER and mitochondria
• abundance of SER and mitochondria
• lack of secretory granules
• some have a long life; hence contain an abundance of lysosomes (help destroy invading organisms and bacteria) and lipofuscin (pigmented residue of lysosomal digesetion)
• if beyond repair, lysosomes help cell self-destruct via apoptosis
• lipid hormones not stored in vesicles as they are lipid soluble