Hormones & the Endocrine System Flashcards
What is a hormone? (definition)
a chemical messenger that is released into the blood stream or tissue fluid system that affects the function of target cells some distance from the source
Endocrine system is…
a form of chemical communication via chemical message hormones
Endocrine cells
- ductless
- located throughout the body; not connected
- secrete hormones into the bloodstream
- integration of hormone production under regulation by the hypothalamus
Exocrine cells
- secrete their products through ducts
- e.g. sweat glands
What are hormones?
- chemical products
- released from endocrine glands
- released into the blood stream
- target cells have receptors (i.e. docking molecules)
4 classes of hormones
- protein or peptide hormones (e.g. insulin)
- steroid hormones (synthesised from cholesterol)
- monamines (e.g. melatonin)
- lipid-based hormones (e.g. prostaglandins)
modes of hormone action (2)
Activational effects:
- short-term, reversible effects that occur in the fully developed organism (e.g. oxytocin and maternal behaviour)
Organisational effects:
- long-term, irreversible effects on tissue differentiation and development (e.g. brain, ovary) that can either directly (brain) or indirectly (ovary) influence behaviour
- critical or sensitive period (e.g. fetal development, puberty)
Activational effects of hormones
e.g. oxytocin and maternal behaviour in rats
- pre maternal mice attack pups
- oxytocin injections induce maternal behaviour
Organisational effects of hormones
- perinatal -> ? -> 2. pubertal/adolescent
sexual differentiation via exposure to steroids during development
mechanisms of hormone release
(a) humoral
(b) neural
(c) hormonal
(a) capillary blood contains low concentration of Ca2+, which stimulates secretion of parathyroid hormone (PTH) - parathyroid glands secrete parathyroid hormone
(b) preganglionic SNS fiber stimulates adrenal medulla cells to secrete catecholamines (nerves are included)
(c) the hypothalamus secretes hormone that stimulate the anterior pituitary gland to secrete hormones that stimulate other endocrine glands to secrete hormones
feedback mechanisms
negative feedback:
- hormone - (+) -> target tissue -> product -(-)-> endocrine gland -> hormone
- e.g. control of thyroid hormone secretion
positive feedback:
- hormone -(+)-> target tissue -> product -(+)-> endocrine gland -> hormone
- e.g. contractions in childbirth (Oxytocin)
hypothalamus
- part of the brain that controls anterior pituitary hormone release
- neurohormones -> released from nerve cell terminals into blood vessels in pituitary gland
The pituitary gland (= Hypophysis)
- anterior pituitary (Adenohypophysis)
- posterior pituitary (Neurohypophysis)
Hypothalamus & Pituitary Gland overview
6 hormones from anterior lobe of pituaitary gland that either inhibit or release hormone:
1. ACTH -> adrenal cortex -> Glucocorticoids (steroid hormones)
2. TSH -> thyroid gland -> thyroid hormones
3. GH -> liver -> somatomedins -> bones, muscles, and other tissues
4. PRL -> mammary glands
5. FSH + LH -> testes of male -> inhibin, testosterone
6. LH + FSH -> ovaries of female -> estrogen, progesterone, inhibin
2 hormones produced in hypothalamus but stored and released from posterior pituitary gland:
1. ADH -> kidneys
2. OXT -> females: uterine smooth muscle and mammary glands, males: smooth muscle in ductus deferens and prostate gland
Releasing and Tropic hormones
releasing:
1. Thyrotropic releasing hormone (TRH)
2. Corticotropin releasing hormone (CRH)
3. Gonadotropin releasing hormone (GnRH)
4. Prolactin releasing factor (PRF)
5. Growth hormone releasing hormone (GHRH = Somatocrinin)
inhibiting:
6. Prolactin inhibiting factor (PIF)
7. GH inhibiting hormone (GHIH = Somatostatin)
- turns on TSH (Thyroid-stimulating hormone)
- turns on ACTH (Adrenocorticotropic hormone)
- turns on FSH and LH (Follicle-stimulating hormone, and Luteinizing hormone)
- turns on PRL (prolactin)
- turns on GH (growth hormone)
- turns off PRL (prolactin)
- turns off GH (Growth Hormone)
Adenohypophysal hormones (anterior pituitary)
Tropic hormones:
- thyroid-stimulating hormone (TSH): stimulates the thyroid gland to produce thyroid hormones
- Adrenocorticotropic hormone (ACTH): stimulates the adrenal cortex to produce corticosteroids (aldosterone and cortisol)
- Follicle-stimulating hormone (FSH): stimulates follicle growth and ovarian oestrogen production, and sperm production
- Luteinizing hormone (LH): has a role in ovulation and the growth of the corpus luteum; stimulates androgen secretion in testes
Adenohypophysal hormones (anterior pituitary)
Non-tropic hormones:
- Growth hormone (GH): protein hormone; effects on growth (bones, muscles) and metabolism (protein, fat, and carbohydrate metabolism)
- Prolactin (PL): protein hormone; stimulates mammary gland development, milk production and reproduction (parental care); effects of immune functions
Prolactin - Endocrine Analogies
prolactin not only necessary in mammary glands, also important in food production
- discus milk
- crop milk production in birds
endocrine regulation of endogenously produced food for young
Neurohypophysial hormones (posterior pituitary)
- ADH: Antidiuretic hormone (= Vasopressin) - helps to retain water in body and to constrict blood vessels; also has behavioural effects, particularly in aggression and territoriality
- Oxytocin: important role for intimacy, specifically in sexual reproduction of both sexes, in particular during and after childbirth; “bonding hormone” (maternal and paternal care)
Endocrine regulation of fluid balance
- ADH is produced in the hypothalamus, stored in posterior pituitary gland, and released into the bloodstream in response to changes in blood osmolarity or blood volume
- ADH regulates fluid balance in the body by controlling the amount of water reabsorbed by the kidneys
- if concentration of salts etc goes up in blood - indicated dehydration - ADH present
OT, ADH, & Social Behaviour
- OT and ADH (peptide hormones) modulate several aspects of social behaviours
- OT promotes maternal nurturing and bonding, enhances social reward, and increases the salience of social stimuli
- ADH modulates social communication, social investigation, territorial behaviour, and aggression, predominantly in males
- both peptides facilitate social memory and pair bonding behaviours in monogamous species
- both peptides modulate parental care
oxytocin & lactation
- stimulation of nipple -> brain activity in mother
- hypothalamus receives sensory information
- oxytocin released from posterior pituitary
- oxytocin causes cells of mammary glands to contract -> release of milk
Oxytocin & Labour
- during labour, the fetus’s head pushes on the cervix, which stimulates the brain to release oxytocin
- oxytocin causes the uterus muscles to contract, which stimulates the brain to release more oxytocin -> increases in frequency and intensity of contractions (positive feedback)
- oxytocin also increases the production of prostaglandins ( -> increase in contractions)
