Endocrine system Flashcards
Endocrine glands
clusters of cells that release products directly into blood because they are ductless – they have to be highly vascularized and their cells have extensive rER and sER because their main function is production of proteins and lipids (hormones)
How do hormones act? Give examples
What is homeostasis?
They bind to a specific receptor on the cells of the target tissue and change its metabolic activity
the pituitary gland releases FSH, it reaches tissue inside ovaries and stimulates cells to produce oestrogen (smooth ER activated, steroid hormone) – an example of negative feedback mechanism because if the oestrogen level in the blood is too low, the pituitary gland will continue producing FSH to stimulate ovaries
the maintenance of the internal environment (variables of body fluids, e.g. water balance = osmoregulation) between narrow and defined limits
Pancreas – function
An endo and an exocrine gland located below the stomach from which digestive enzymes are released via pancreatic duct into the beginning of the small intestine (amylase, protease, nuclease and lipase) – between exocrine glands and ducts in the pancreas there are islets of Langerhans which are clusters of endocrine cells
There are two types of endocrine cells: alpha cells that produce glucagon (liver and muscle cells targeted) and beta cells that produce insulin (all cells). Islets are separated from the surrounding exocrine tissue by a thin capsule. They are extensively vascularized; an islet is a capillary bed surrounded by secretory cells
What is the set range for blood glucose concentration – how is it maintained?
4-8 mmol/L
Chemoreceptors in the pancreas are responsible for regulating glucose level, two situations:
1) Level is too high (eating sugar), beta cells stimulated to release insulin into the blood. 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) Level is too low (exercising, skipping meals), alpha cells activated to release glucagon into the blood. Only liver and muscle cells are affected in this case as glucagon will enter them and hydrolyze glycogen into glucose. Glucose will be released into the blood and its levels raised
Possible causes of diabetes – types. How does the glucose level in blood differ in diabetic patients from the normal level. How are they affected differently by a spike in glucose?
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
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 conditions are present in both types of 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 metabolized in cell respiration
Hormones – types, their function
chemical messengers produced by endocrine glands that travel through blood and affect target tissue – they can be steroids, peptide derivatives or tyrosine derivatives
Steroid hormones
- testosterone and oestrogen
- derivatives of cholesterol
- pass through the membrane
- receptor protein in the cytoplasm or nucleus (hormone-receptor complex)
- affect gene expression by binding to the promotor region of a specific gene
- cause production/absence of specific enzymes (or other proteins)
- effect is slower and more permanent
Peptide hormones
- ADH (antidiuretic hormone), insulin, calcitonin, melatonin, epinephrine
- 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
tyrosine derivatives
- thyroxin, thyroid hormones like T3 and T4
- speed up CR (when there is a lack of them, the person is tired)
How is circadian rhythm set/maintained?
set by groups of cells in the hypothalamus called the suprachiasmatic nuclei (SCN) that control the secretion of hormone melatonin by the pineal gland
melatonin secretion increases in the evening and drops to a low level at dawn when 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)
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)
Epinephrine (adrenaline) secretion – effects on the body
controlled by the brain and secreted by adrenal glands
triggers responses in a wide range of cells that collectively prepare 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 and 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
Hypothalamus – two types of neurons – division onto regions
Nervous tissue made of thousands of neurosecretory cells that links the nervous system to the endocrine system via the pituitary gland
Long-ending neurosecretory cells end in the posterior lobe of the pituitary gland
Short-ending release neurohormones in the capillary network that joins into a blood vessel called the portal vein that branches into another network to supply the anterior pituitary lobe
Nuclei are specialized regions inside the hypothalamus that control specific autonomic processes like thermoregulation (thermoreceptors), blood pressure, osmoregulation (baroreceptors) and secretion of pituitary hormones. Nuclei can receive signals from medulla oblongata, from sense organs either directly or indirectly via the cerebral hemispheres
Pituitary gland – function of both lobes described
endocrine gland that is part of the nervous system
anterior lobe:
- Ventral
- Neurohormones called releasing hormones are sent from the hypothalamus to APL via portal vein
- Releasing hormones stimulate endocrine cells in APL to produce and release their own hormones by exocytosis
- Examples: TSH (thyroid stimulating hormone), gonadotropins (FSH and LH), GH, and PRL
Posterior lobe
- Dorsal
- Physical extension of the hypothalamus
- Neurohormones synthesized in the neurosecretory cells and transported and stored in vesicle sin the axon ending located in PPL
- When a nerve impulse travels down the axon from the hypothalamus, neurohormones get released into the blood
- Examples: ADH (reduced V of urine), oxytocin (in uterine muscles and mammary glands, rapid and short-lasting)
Thyroxin release
- Nucleus in the hypothalamus receives info on low thyroxin concentration
- It releases TSH into APL
- APL releases TSH into the capillary network to the thyroid gland which will produce more thyroxin and stimulate all body cells
- Results in increased activity of cells (CR increased) and increased metabolism (negative feedback mechanism)
Compare and contrast hormonal and neural signaling
Type of signal: chemical vs electrical
Transmission route: blood vs neurons
Destination of the signal: widespread but only target cells respond vs only specific cells connected via synapse
Effectors: target cells vs muscles/glands
Speed of response: slower vs very rapid
Duration of response: long duration (until hormone breakdown) vs short duration (unless impulses repeatedly sent)
Types of response:
H – growth, development (puberty), reproduction (pregnancy), changes in metabolic rate and sleep (mood), changes in concentrations of solute in blood
N – contraction of striated/smooth muscles, change to the rate of cardiac muscle contraction, galdn secretion
Thermoregulation mechanism
- Both endocrine and nervous control
- Negative feedback mechanism
- Receptors: peripheral thermoreceptors in the skin, central receptors in the hypothalamus
- Target cells/effectors: main targets are muscles, adipose tissue, liver, blood vessels, thyroid gland (thyroxine increases the level of CR in all cells) and brain
How is hyperthermia battled?
Blood temp above regulation point
a) sweat glands in the dermis activated (smooth muscles constrict around the gland, causing the release of sweat)
b) vasodilation (hot blood flows faster and goes from vessels to skin more rapidly)
c) moving away from the heat source and moving more slowly and sleeping longer (behavioral)
How is hypothermia battled?
Blood temp below regulation point
a) shivering of skeletal muscles (involuntary contraction and relaxation, heat produced by CR)
b) vasoconstriction (storing E inside the body)
c) brown adipose tissue (has more mitochondria than white adipose tissue and goes through uncoupled CR where no ATP is produced, only heat – as we age, we lose brown adipose tissue)
d) hair erection (thicker layer of insulation, not in humans, poli erector muscle activated)
e) moving faster to generate more heat (behavioral)
Blood supply differences during 1) intense physical activity 2) wakeful rest 3) sleep
1) increased BS to skeletal muscles and brain to supply more O2 and glucose for muscle contraction, mental activity heightened – reduced to the gut and kidneys, digestion and excretion suspended
2) max BS to kidneys, moderate to brain and skeletal muscles, variable to digestive system
3) increased BS in the brain (releasing toxins from the brain, regulating circadian rhythms), reduced to skeletal muscles, kidneys, variable to digestive system
