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Questions and Answers
Which of the following hormones is released from the stomach wall when it is empty?
Which of the following hormones is released from the stomach wall when it is empty?
What is the primary function of the arcuate nucleus in the hypothalamus?
What is the primary function of the arcuate nucleus in the hypothalamus?
What is the effect of ghrelin on the excitatory primary neurones in the arcuate nucleus?
What is the effect of ghrelin on the excitatory primary neurones in the arcuate nucleus?
What is the effect of PYY on the excitatory primary neurones in the arcuate nucleus?
What is the effect of PYY on the excitatory primary neurones in the arcuate nucleus?
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What is the primary function of pro-opiomelanocortin (POMC) in the arcuate nucleus?
What is the primary function of pro-opiomelanocortin (POMC) in the arcuate nucleus?
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What is the effect of filling the stomach on ghrelin release?
What is the effect of filling the stomach on ghrelin release?
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What is the primary function of the glucocorticoids in the adrenal cortex?
What is the primary function of the glucocorticoids in the adrenal cortex?
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What is the effect of insulin on glucose uptake in cells?
What is the effect of insulin on glucose uptake in cells?
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What is the primary function of glucagon in glucose regulation?
What is the primary function of glucagon in glucose regulation?
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What is the net effect of energy intake exceeding energy expenditure?
What is the net effect of energy intake exceeding energy expenditure?
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What is the primary function of leptin in the regulation of appetite?
What is the primary function of leptin in the regulation of appetite?
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What is the approximate percentage of endocrine tissue in the pancreas?
What is the approximate percentage of endocrine tissue in the pancreas?
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What is the primary function of the exocrine pancreas?
What is the primary function of the exocrine pancreas?
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What is the effect of amylin on glucagon secretion?
What is the effect of amylin on glucagon secretion?
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What is the embryological origin of the pancreas?
What is the embryological origin of the pancreas?
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What is the primary function of the receptor in homeostasis?
What is the primary function of the receptor in homeostasis?
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What is the effect of insulin on appetite?
What is the effect of insulin on appetite?
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How do endocrine hormones typically travel in the body?
How do endocrine hormones typically travel in the body?
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What is the role of UCP (uncoupling proteins) in the regulation of energy balance?
What is the role of UCP (uncoupling proteins) in the regulation of energy balance?
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What is the primary mechanism of controlling hormone secretion?
What is the primary mechanism of controlling hormone secretion?
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What is the term for the resistance to the effects of leptin in obese individuals?
What is the term for the resistance to the effects of leptin in obese individuals?
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What is the characteristic of hormone concentrations in the blood?
What is the characteristic of hormone concentrations in the blood?
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What is the function of the effector in homeostasis?
What is the function of the effector in homeostasis?
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What is the characteristic of peptide and amine hormones in terms of transportation in the blood?
What is the characteristic of peptide and amine hormones in terms of transportation in the blood?
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What is the function of the control centre in homeostasis?
What is the function of the control centre in homeostasis?
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What is the process that inactivates hormones in the body?
What is the process that inactivates hormones in the body?
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Study Notes
Steroid Hormones and Energy Balance
- C21 steroids: corticosteroids (glucocorticoids, e.g., cortisol, and mineralocorticoids, e.g., aldosterone) and progestins (e.g., progesterone from ovaries)
- C19 steroids: androgens (e.g., testosterone from testes)
- C18 steroids: oestrogens (e.g., oestradiol from ovaries)
Hormone Action
- Hormones act by binding to receptors on or in target cells
- Magnitude of response depends on: hormone concentration, receptor number, hormone-receptor affinity, and signal amplification
- If hormone cannot cross membrane, it binds to cell surface receptor, activates second messenger pathway, and exerts metabolic effects
Mechanism of Action of Steroid Hormones
- Steroid hormones bind to receptors in target cells, leading to changes in gene expression and protein synthesis
Control of Energy Balance
- Energy balance: energy intake = expenditure (stable body weight), energy intake > expenditure (increased energy stores), energy expenditure > intake (decreased energy stores)
- Appetite control centre: hypothalamus, containing clusters of neurons (nuclei), including the arcuate nucleus
Control of Appetite
- Arcuate nucleus contains two types of neurons: primary (sense glucose, fatty acids, and hormones) and secondary (integrate signals for feeding behavior)
- Primary neurons: stimulatory (excitatory, containing NPY and AgRP) and inhibitory (containing POMC, alpha-MSH, and beta-endorphin)
- Ghrelin: released from stomach wall when empty, stimulates appetite, and inhibited by stomach distension
- PYY (Peptide tyrosine tyrosine): released from ileum and colon in response to feeding, inhibits appetite, and signals satiety
Hormonal Signals
- Leptin: released from fat cells, suppresses appetite, and stimulates POMC neurons in the arcuate nucleus
- Insulin: suppresses appetite by similar mechanism as leptin
- Amylin: secreted by pancreatic beta cells, suppresses appetite, decreases glucagon secretion, and slows gastric emptying
Other Players and Therapeutics
- Large intestine: oxyntomodulin, GLP-1
- Small intestine: cholecystokinin, GIP
- Adipose: adiponectin, resistin, visfatin
- Pancreas: PP (Pancreatic polypeptide)
Integration of Energy Balance
- Leptin: discovery, role in energy balance, and response to injection in leptin-deficient individuals
Pancreas
- Anatomy: retro-peritoneal gland, majority exocrine, highly vascular and innervated
- Development: embryological origin from the foregut, similar to the brain
- Exocrine function: 98-99% secretion of enzymes for digestion of lipids, carbohydrates, and proteins
- Endocrine function: 1-2% of pancreatic mass, hormone production
Homeostasis
- Control centre: hypothalamus, determines reference set point
- Receptor: sensors detect changes in the environment
- Effector: agents cause change
- Feedback: output affects the control centre
Endocrine Hormones
- Definition: chemical signals produced in endocrine glands or tissues that travel in the bloodstream to cause an effect on other tissues
- Release: from endocrine glands, travel in blood stream, interact with receptors, and cause coordinated responses
Glands of the Endocrine System
- Endocrine tissue: pancreas, thyroid, adrenal glands, etc.
- Biologically active chemical: hormones produced by endocrine glands
- Transport: in blood stream
- Target cells: receptors and response
- Inactivation: metabolism of hormone causes inactivation
Control of Hormone Secretion
- Rate of secretion usually controlled by negative feedback: change in parameter regulated by the hormone or concentration of hormone itself or another hormone
Hormone Concentrations
- Hormones circulate in very low concentrations (e.g., thyroxine 10-30 pmol/L)
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Description
Learn about the classification of steroid hormones, including C21, C19, and C18 steroids, and understand how hormones act on target cells.
