5.5. Endocrine system Flashcards
Endocrine glands
clusters of cells that release products directly into blood because they are ductless but highly vascularized, have extensive rER (and sER) because their main function is production of proteins and lipids (hormones)
hormone pathway to tissue (FSH example)
released into blood, binds to a specific receptor on the cells of the target tissue and changes its metabolic activity
the pituitary gland releases FSH, it reaches tissue inside ovaries and stimulates cells to produce oestrogen (smooth ER activated, steroid hormone)
what are hormones. What are different types of hormones?
chemical messengers produced by endocrine glands that travel through blood and affect target tissue
steroids (oestrogen, testosterone), peptide derivatives (insulin) or tyrosine derivatives (thyroid hormones like T3 and T4)
what is homeostasis
maintenance of the internal environment (variables of body fluids) between narrow and defined limits
pancreas structure
located below the stomach, both an endo and exocrine gland
exo: digestive enzymes are released via pancreatic duct into the beginning of the small intestine (amylase, protease, nuclease and lipase)
endo: between exocrine glands and ducts there are islets of Langerhans (clusters of endocrine cells), two types of endocrine cells: alpha cells (glucagon) and beta cells (insulin), islets are separated from the exocrine tissue by a thin capsule and are extensively vascularized
glucose blood concentration regulation
Set range for blood glucose concentration is 4-8 mmol/L.
If the level is too high (eating sugar), beta cells in islets are stimulated and they release insulin into the blood (targeting all body cells). Body cells absorb glucose through glucose channels and use it for cell respiration (more E produced). Liver and muscle cells will do the same but most of glucose will be polymerized and stored as glycogen.
If the level is too low (exercising, skipping meals), alpha cells will be activated, and glucagon will be released into the blood. Only liver and muscle cells are affected in this case as glucagon will enter them and hydrolyse glycogen into glucose. Glucose will be released into the blood and thus its levels will be raised.
Which cells don’t have to be stimulated by pancreas to take up glucose?
brain cells and intestinal cells
Difference in pancreas action when the glucose level is too high vs too low.
1) If the level is too high (eating sugar), beta cells in islets are stimulated and they release insulin into the blood (targeting all body cells). Body cells absorb glucose through glucose channels and use it for cell respiration (more E produced). Liver and muscle cells will do the same but most of glucose will be polymerized and stored as glycogen.
Not all body cells have to be stimulated by pancreas to take up glucose. For example, brain cells and intestinal cells.
2) If the level is too low (exercising, skipping meals), alpha cells will be activated, and glucagon will be released into the blood. Only liver and muscle cells are affected in this case as glucagon will enter them and hydrolyse glycogen into glucose. Glucose will be released into the blood and thus its levels will be raised.
What can be causes of diabetes:
1) complete lack of insulin – type I, juvenile, early-onset
2) insufficient amount of insulin – type II, late-onset
3) reduced sensitivity of target cells to insulin – type II, late-onset
How do diabetic patients’ levels of glucose differ from healthy?
Diabetic patients have a higher initial concentration of glucose in blood and it takes longer for the concentration to get back to the initial range after a spike in glucose.
What is present in both type I and type II diabetes?
a) A build of glucose in blood (hyperglycaemia) – high osmotic pressure – movement of water from cells by osmosis into blood – high blood pressure – larger quantities of urine
b) Lack of glucose in cells – disbalance in the metabolism of the food molecules, first fats followed by proteins have to be metabolised in cell respiration
Steroid hormones and peptide hormones
- structure
- location of the receptor on the target cell
- their effect on the target cell
- the longevity and speed of the effect
- examples
- derivatives of cholesterol
- pass through the membrane to the receptor protein in the cytoplasm or nucleus (hormone-receptor complex)
- affect gene expression by binding to the promotor region of a specific gene
- production/absence of specific enzymes (or other proteins)
- the effect is slower and more permanent
- testosterone and oestrogen
- made of amino acids
- attach to membrane receptor on the cell surface
- secondary messenger triggers reactions that stimulate or inhibit enzyme production
- rapid and temporary effects
- ADH (antidiuretic hormone) and calcitonin, melatonin, epinephrine
What is circadian rhythm and what is it set by?
How exactly?
What is the process of impulse propagation?
What secretes melatonin?
How does melatonin secretion change?
What is its function?
Circadian rhythm diurnal and nocturnal phases) is set by groups of cells in the hypothalamus called the suprachiasmatic nuclei (SCN) that control the secretion of hormone melatonin by the pineal gland.
A special type of ganglion cell in the retina detects light and passes impulses to SCN which adjusts melatonin secretion accordingly (less melatonin as we age)
Increases in the evening and drops to a low level at dawn, it is rapidly removed from the blood by the liver.
High melatonin levels promote sleep through the night and falling melatonin levels encourage waking at the end of the night
What is epinephrine and what is its effect?
What responses and target cells does it activate?
Fight or flight hormone resulting in striated muscles receiving more and more glucose and oxygen-rich blood, allowing increased production of ATP and thus more frequent and powerful muscle contractions (preparing the body for vigorous activity)
1. Striated muscle fibres convert stored glycogen into glucose (supplies for CR)
2. Liver cells convert glycogen to glucose and release it into blood to muscles
3. Bronchioles dilate due to relaxation of smooth muscle cells (easier ventilation)
4. Cells in the brainstem (controlling ventilation) stimulate intercostal muscles and diaphragm to contract at a faster rate ad more forcefully (increasing gas exchange)
5. Sinoatrial node speeds up the heart rate (cardiac output increases)
6. Arterioles carrying blood to muscles and liver vasodilate due to relaxation of smooth muscle cells in their walls
7. Arterioles carrying blood to the gut, kidneys and skin vasoconstrict due to contraction of smooth muscle cells in their walls
What is the hypothalamus?
What processes do its nuclei control?
Where do they receive signals from?
Nervous tissue that links the nervous system to the endocrine system via the pituitary gland. Made out of thousands of neurosecretory cells (long- in the posterior lobe and short-ending in the anterior lobe).
A) Thermoregulation (nucleus with thermoreceptors)
B) Blood pressure
C) Osmoregulation (nucleus with glucose and baroreceptors)
D) Secretion of pituitary hormones
Some nuclei receive signals from sense organs either directly or indirectly via the cerebral hemispheres. There are also inputs from other parts of the brain like medulla oblongata.
