Introduction to endocrinology Flashcards
Define homeostasis
Maintenance of steady state of internal environment
Give examples of variables controlled by homeostasis
Physical entities:
- Blood pressure
- Core temperature
Circulating concentrations of chemical substances:
- Ions, e.g. Na+, Ca2+
- Nutrients e.g. blood glucose concentration
- Hormones
Briefly outline how negative feedback works when body temp changes
There’s a set point at which body temp should be (With infection, the set point is changed and body temp rises)
Change in body temp detected by hypothalmic temperature receptors and/or cutaneous temperature receptors (on skin, these can induce thermoregulatory effects)
Hypothalamus induces negative feedback, if heat needs to be lost, vasodilation occurs to allow evaporation of water via sweating
If heat needs to be gained, muscles begin shivering, vasoconstriction occurs to reduce heat loss, increased metabolism to bring body back to core body temperature
What are the benefits of an increased body temp and what causes an increase in body temp?
Pyrogens (bacteria or virus infections) change the set point to a higher level resulting in fever
Benefits are:
- Inhibits bacterial growth
- Speeds up metabolic reactions
- Increases delivery of WBCs to infection sites
How is body temp increased?
- Blood flow shifted to core to conserve heat
- Increased muscle activity (shivering)
- Chills stop when high temp reached
Describe the baroreceptor reflex
Homeostatic control of blood pressure
Change in BP detected by baroreceptors, which can tell how much the arteriole walls have deformed/stretched, and therefore can tell when there’s a change in TPR
Baroreceptors signal medulla
Medulla signals heart and TPR is adjusted accordingly
Describe how hypertension can effect blood pressure regulation
Hypertension causes resetting of sensitivity of baroreceptors, making them more sensitive.
How are cortisol concentrations controlled?
- Hypothalamus receives impulse, releases CRH on anterior pituitary glad
- Anterior pituitary gland releases ACTH on adrenal cortex
- Adrenal cortex secretes cortisol
What is positive feedback?
Response of effector output reinforces the stimulus (e.g. blood clotting, ovulation, childbirth)
Describe the role of positive feedback in control of uterine contraction in labour by oxytocin
- In labour oxytocin stimulates uterine muscle contractions
- Cervix dilates, activates stretch receptors
- Action potentials signal to hypothalamus
- Stimulates further release of oxytocin
What are the major endocrine glands? Describe their anatomical locations
- Pineal - Deep in middle brain
- Hypothalamus - Superior to midbrain, inferior to thalamus (Part of the diencephalon)
- Pituitary - Within sella turcica of neurocranium
- Thyroid - Superficial to trachea
- Parathyroid - Next to 2 thyroid glands (lateral)
- Adrenal - Superior to kidneys
- Pancreas - Deep to stomach
- Ovaries (women) - Lower abdomen, on right and left sides of uterus
- Testes (men) - underneath penis
What does the hypothalamus do?
Releases and inhibits hormones
What does the anterior lobe of the pituitary gland release?
Trophic hormones
What does the posterior lobe of the pituitary gland release?
Oxytocin and vasopressin (ADH)
What does the thyroid gland release?
Thyroxine (T4)
Tri-iodothyronine (T3)
What does the adrenal cortex release?
- Cortisol
- Aldosterone
What does the adrenal medulla release?
Adrenaline/noradrenaline
What do the gonads release?
Oestrogen
Androgens
Progestagens
What does the pancreas release?
- Insulin
- Glucagon
What does the parathyroid gland release?
Parathyroid hormone
Describe the endocrine signalling mechanism
Hormones released by an endocrine cell into general circulation and act on distant target sites
Describe the paracrine signalling mechanism
Hormones released by an endocrine cell which act locally on adjacent cells
Describe the autocrine signalling mechanism
Hormones released by a cell which act back on the same cell
Describe the intracrine signalling mechanism
Conversion of an inactive hormone to an active hormone that acts within that cell
What are the general functions of hormones?
- Reproduction, growth, development - sex steroids, thyroid hormones, prolactin, growth hormone
- Maintenance of internal environment - Aldosterone, parathyroid hormone, vitamin D
- Energy production, utilisation and storage - Insulin, glucagon, thyroid hormones, cortisol, growth hormone
Describe the 4 chemical classes of hormone
Protein/peptide hormones - Hypothalmic hormones (exceptions Dopamine), pituitary hormones, insulin, PTH, Calcitonin
Steroid hormones (cholesterol) - Cortisol, aldosterone, oestrogens, androgens, progestagens, vitamin D
Amino acid derivatives (tyrosine/tryptop han) - Adrenaline, noradrenaline, dopamine (tyrosine), thyroid hormones (tyrosine), Melatonin (trytophan)
Fatty acid derivatives - Prostaglandins, thromboxanes, prostacyclin
Describe the nature of transport of protein and peptide hormones. What is their half-life?
Mainly unbound
Half life in circulation = minutes
Describe the nature of transport of tyrosine derivatives (catecholamines), thyroid hormones. What is their half-life?
Thyroid hormones bound to plasma proteins
Half life in circulation = Seconds (catecholamines), hours (thyroid hormones)
Describe the nature of transport of Cholesterol derivations (all steroids) What is their half-life?
Bound to plasma proteins
Half life in circulation = hours-days
Define a neurosecretory cell
Neurones that secrete substances directly into the bloodstream to act as hormones
What is the function of magnocellular neurones? What do other neurosecretory cells in the hypothalamus release?
In hypothalamus
Synthesise and release posterior pituitary hormones
Other neurosecretory cells release their hormones into the portal capillaries in which they are transported directly to endocrine cells of the anterior pituitary gland
What is the effect of corticotrophin releasing hormone (CRH) released by the hypothalamus on the anterior pituitary gland?
Stimulates release of adrenocorticotrophic hormone (ACTH)
What is the effect of Thyroid releasing hormone (TRH) released by the hypothalamus on the anterior pituitary gland?
Stimulates release of TSH (thyroid stimulating hormone
What is the effect of Growth hormone inhibiting hormone (GHIH - somatostatin) released by the hypothalamus on the anterior pituitary gland?
Inhibits release of TSH
What is the effect of Gonadotrophin releasing hormone (GnRH) released by the hypothalamus on the anterior pituitary gland?
Stimulates release of Luteinising hormone (LH) and follicle stimulating hormone (FSH)
What is the effect of Dopamine released by the hypothalamus on the anterior pituitary gland?
Inhibits release of prolactin (PRL)
What is the effect of Growth hormone releasing hormone (GHRH) released by the hypothalamus on the anterior pituitary gland?
Stimulates release of growth hormone (GH)
What is the effect of Growth hormone inhibiting hormone (somatostatin) released by the hypothalamus on the anterior pituitary gland?
Inhibits release of growth hormone (GH)
What are the peripheral endocrine glands controlled by the HPA?
Thyroid
Adrenal cortex
Gonads
