SNS - Biology - Endocrimology Flashcards
Hormones
Peptides
Examples
- ADH – simple, short peptide
- Insulin – complex polypeptide
Hormones
Steroid
Examples
- Oestrogen
- Aldosterone
Endocrine Glands
A-H
Secrete hormones directly into bloodstream
- Adrenals
- GI glands
- Heart
- Hypothalamus
Endocrine Glands
I-P
- Kidney
- Pancreas
- Parathyroids
- Pineal
- Pituitary
Endocrine Glands
Q-Z
- Ovaries
- Testes
- Thymus
- Thyroid
Endocrine Glands
Adrenal
Situated on top of the kidneys
Consist of cortex and medulla
Endocrine Glands
Adrenal
Cortex
- Anterior pituitary releases ACTH in response to stress, stimulating the adrenal cortex to synthesise and secret corticosteroid hormones – glucocorticoids and sex steroids
- Renin-angiotensin mechanism controls production of aldosterone
Corticosteroids
- Glucocorticoids
- Mineralocorticoids
- Cortical sex hormones
Corticosteroids
Glucocorticoids
- Cortisol, cortisone
- Involved in glucose regulation and protein metabolism – raise blood glucose levels by promoting protein breakdown and using the products for gluconeogenesis as well as decreasing protein synthesis
Corticosteroids
Mineralocorticoids
- eg Aldosterone
- Regulate plasma levels of sodium and potassium and thus extracellular fluid volume
- Causes active reabsorption of sodium and passive reabsorption of water in the nephron, increasing blood volume and BP.
- Excess aldosterone results in hypertension therefore
Corticosteroids
Cortical Sex Hormones
- Adrenal cortex secretes small amounts of androgens with androstenedione and dehydroepiandrosterone in both males and females
- In males, most androgens produced by testes, in females however, overproduction can have masculinising effects
Endocrine Glands
Adrenal
Medulla
- Produces catecholamines (adrenaline and noradrenaline)
- Adrenaline increases conversion of glycogen to glucose in liver and muscle tissue
- Both NA and adrenaline increase heart rate and force and dilute and constrict blood vessels in such a way as to increase blood supply to skeletal muscle, heart and brain and decrease supply to kidneys, skin and digestive tract
Endocrine Glands
Pituitary
- Small, trilobed structure at base of brain
- Two main lobes – anterior and posterior
- Third lobe – intermediate – is rudimentary
Endocrine Glands
Pituitary
Anterior
- Synthesises both direct and trophic hormones
- Regulated by hypothalamic secretions – releasing or inhibiting hormones/factors
Endocrine Glands
Pituitary
Anterior
Direct Hormones
Directly stimulate target organs
- GH – bone and muscle growth
- Endorphins – NTs which behave like opioids
- Prolactin – stimulates milk production and secretion in female mammary glands
Endocrine Glands
Pituitary
Anterior
Trophic Hormones
Stimulate other endocrine glands to release hormones
- ACTH – stimulates adrenal cortex to secrete glucocorticoids. Regulated by CRF
- TSH = stimulates thyroid to release thyroid hormones such as thyroxine
- LH – stimulates ovulation and formation of corpus luteum in females. Stimulates interstitial cells of testes to synthesise testosterone in males
- FSH – stimulates maturation of ovarian follicles and secretion of oestrogen in females. Stimulates maturation of seminiferous tubules and sperm production in males
Endocrine Glands
Pituitary
Posterior
• Neurohypophysis
• Doesn’t synthesize but stores and releases peptide hormones produced by neurosecretory cells of the hypothalamus upon AP from hypothalamus
1. Oxytocin
2. ADH
Endocrine Glands
Pituitary
Posterior
Oxytocin
- Secreted during childbirth
- Increases strength and frequency of uterine contractions
- Positive feedback mechanism – oxytocin release causes uterine contraction which in turn stimulates the release of more oxytocin. Continues until the child is born
- Secretion also induced by suckling, as stimulates milk secretion in the mammary glands
Endocrine Glands
Pituitary
Posterior
ADH
- Increases the permeability of the collecting duct in the nephron to water, promoting water reabsorption and decreasing blood osmolarity by increasing blood volume
- Secreted when plasma osmolarity increases, as sensed by osmoreceptors in the hypothalamus, or in response to decreased blood volume as sensed by baroreceptors in the circulatory system
Endocrine Glands
Hypothalamus
- Receives neural transmission from other parts of the brain and peripheral nerves which trigger specific responses from neurosecretory cells
- Neurosecretory cells regulate pituitary gland secretions via negative feedback and via actions of inhibiting and releasing hormones
Endocrine Glands
Hypothalamus
Interaction With Posterior Pituitary
• Neurosecretory cells of the hypothalamus synthesize both oxytocin and ADH and transport them via their axons into the posterior pituitary for storage and release
Endocrine Glands
Hypothalamus
Interaction With Anterior Pituitary
- Releasing hormones stimulate or inhibit secretions of the anterior pituitary
- For example, GnRH stimulates release of LH and FSH
- Releasing hormones are secreted into the hypothalamic-hypophyseal portal system – circulatory pathway from capillaries of the hypothalamus via the portal vein into the anterior pituitary where diverges into a second capillary network
Endocrine Glands
Thyroid
- Bi-lobed structure located in the ventral surface of the trachea
- Produces and secretes thyroxine and tri-iodothyronine (thyroid hormones) and calcitonin
Endocrine Glands
Thyroid
Thyroid Hormones
- Thyroxine (T4) and tri-iodothyronine (T3)
- Derived from iodination of tyrosine
- Necessary for growth and neurological development in children
- Increase rate of metabolism in the body
Hypothyroidism
- Little or no secretion of thyroid hormones
- Symptoms include slowed heart rate and respiratory rate, fatigue, cold intolerance, weight gain
Cretinism
Hypothyroidism in newborns
Characterised by mental retardation and short stature
Hyperthyroidism
- Thyroid over stimulated, resulting in oversecretion of thyroid hormones
- Symptoms include increased metabolic rate, excessive warmth, sweating, palpitations, weight loss, protruding eyes
- Thyroid often enlarges – goitre
Endocrine Glands
Thyroid
Calcitonin
- Decreases plasma Ca2+ by inhibiting release of Ca2+ from the bone
- Secretion regulated by plasma Ca2+ levels
- Antagonistic to parathyroid hormone
Endocrine Glands
Pancreas
- Both exocrine and endocrine
- Exocrine – performed by cells that secrete digestive enzymes into the small intestines via series of ducts
- Endocrine – performed by small glandular structures – islets of Langerhans, composed of alpha and beta cells which secrete glucagon and insulin respectively
Endocrine Glands
Pancreas
Glucagon
Stimulates protein and fat degradation, conversion of glycogen to glucose and gluconeogenesis
Serves to increase blood glucose
Endocrine Glands
Pancreas
Insulin
Protein hormone secreted in response to high blood glucose
Stimulates uptake of glucose by muscle and adipose cells, synthesis of fats from glucose and storage of glucose as glycogen in muscle and liver cells
Serves to decrease blood glucose
Antagonistic to glucagon, glucocorticoids, GH and adrenaline
Endocrine Glands
Parathyroid
- Four small, pea shaped structures embedded in the posterior surface of the thyroid
- Synthesize and secrete parathyroid hormone which regulates plasma Ca2+ conc by increasing bone resorption and decreasing Ca2+ excretion in the kidney
- Ca2+ bound to phosphate in bone, so breakdown releases phosphate as well as Ca2+. Parathyroid hormone compensates for this by stimulating excretion by kidneys
Endocrine Glands
Kidneys
- When blood volume falls, secrete renin – converts plasma protein angiotensin to angiotensin I.
- This then converted to angiotensin II which stimulates secretion of aldosterone from adrenal cortex
Endocrine Glands
Gastrointestinal Glands
- Gastrin
- Secretin
- Cholcystokinin
Endocrine Glands
Gastrointestinal Glands
Gastrin
- Ingested food stimulates stomach to release gastrin
- Carried to gastric glands and stimulates to secrete HCl
Endocrine Glands
Gastrointestinal Glands
Secretin
- Released by small intestine when acidic food material enters from the stomach
- Stimulates secretion of alkaline bicarbonate solution which neutralises the acidic chyme
Endocrine Glands
Gastrointestinal Glands
Cholecystokinin
- Released from small intestine in response to the presence of fats.
- Causes contraction of the gallbladder and release of bile into the small intestine.
- Also travels to the brain’s satiation centre to stimulate the sensation of being ‘full’
Endocrine Glands
Pineal Gland
- Tiny structure at the base of the brain
- Secretes melatonin - unclear role in humans but believed to have a role in circadian rhythms
- Secretion regulated by light-dark cycles in the environment
Regulation In Plants
• Primarily involved in regulation of growth. Produced by actively growing parts such as meristematic tissues of apical region of shoots and roots
- Auxins
- Anti-auxins
- Gibberellins
- Ethylene
- Inhibitors
- Kinins
Regulation In Plants
Auxins
- Stimulate the production of new xylem cells from cambium
- Associated with several types of growth pattern
- Phototropism
- Geotropism
- Inhibition of lateral buds
Phototropism
- Tendency of shoots to grow towards light
- When light strikes tip of plant from one side, reduces auxin supply on that side.
- Thus illuminated side grows more slowly than shaded side
- Indoleacetic acid is one auxin associated with phototropism
Geotropism
• Growth of portions of plants towards or away from gravity
Geotropism
Negative
- Causes shoots to grow upwards, away from the acceleration of gravity
- Gravity increases auxin conc on lower side of horizontally placed plant while conc on upper side decreases
- Stimulates cells on lower side to elongate faster than cells of upper side causing the plant to grow vertically
Geotropism
Positive
- Causes roots to grow downwards
- Horizontally placed roots also have higher auxin conc on lower side than upper, but effect is opposite to effect on stems – cells exposed to higher auxin conc are inhibited from growing, causing roots to turn downwards
Inhibition of Lateral Buds
- Auxins produced in terminal bud of plant’s growing tip move downwards in the shoot and inhibit development of lateral buds
- Conversely, auxins initiate the formation of lateral roots while inhibit root elongation
Regulation In Plants
Gibberelins
- Stimulate rapid stem elongation, particularly in plants which normally don’t grow tall
- Inhibit formation of new roots and stimulate production of new phloem cells by the cambium
- Also terminate dormancy of seeds and buds
- Induce some biennial plants to flower during first year of growth
Regulation In Plants
Kinins
- Promote cell division
- For example, kinetin – ratio of kinetin to auxin is particularly important in determination of timing of differentiation of new cells. Action is enhanced when auxin is present
Regulation In Plants
Ethylene
- Stimulates fruit ripening
- Also induces senescence
Regulation In Plants
Inhibitors
- Block cell division and serve important roles in growth regulation
- Particularly important to maintenance of dormancy of lateral buds and seeds during autumn and winter
- Break down gradually with time
- For example, abscisic acid
Regulation In Plants
Anti-Auxins
- Regulate activity of auxins
- For example, indoleacetic acid oxidase regulates conc of indoleacetic acid. Increased conc of indoleacetic acid increases production of indoleacetic acid oxidase
