Homeostasis Flashcards
What are is the control loop achieving equilibrium (4)
- Sensor - sensory input conveyed centrally via Afferent paths
- Central integrator - typically the hypothalamus: determines the level of output appropriate to correct the sensation of deviations from a “set point”
- Effector - “motor” output signals conveyed via Efferent paths
- Feedback inhibition - self-limiting - tending to attenuate; promoting dynamic equilibrium (balance) at the “set point”.
What is the function of the CNS (2)
- regulate the activities of various systems of organs, tissues and cells via multiple efferent pathways
- many pathways originate from a central involuntary control site called the hypothalamus
What are the homeostatic effectors (3)
- Peripheral efferent nerves: somatic (voluntary control) & automatic (involuntary, SNS and PsNS)
- Endocrine axes
- Local reflex loops - cells locally communicating
What happens with water loss (3)
- osmolarity (hypertonic plasma)
- decreased volume (hypovolemic plasma)
- low blood pressure (hypotension)
What is Diabetes insipidus (2)
- inadequate secretion of ADH/AVP
- leading to large volume of dilute urine without glucose
What is Diabetes mellitus (3)
- inadequate secretion of pancreatic insulin
- leading to large of glucose in circulation and urine with or without ketoacidosis.
- Results in lots of thirst/drinking and eating to compensate
What is Addison’s disease (3)
- inadequate secretion of aldosterone
- leading to failure to conserve salt which goes out in the urine taking water with it
What is the sensor in temperature regulation
Thermoreceptors
What is the central integrator in temperature regulation
Hypothalamus
What are the effectors in temperature regulation (4)
- Pituitary → thyroid → promote BMR
- Brainstem → ANS → promote BMR + Brown adipose shivering + vasoconstriction + stop sweating
- Brainstem → ANS → PsNs → vasoconstriction
- Limbic → Somatic → skeletal muscle shivering
How is there feedback inhibition in temperature regulation
Nerves → hypothalamus
What are the sensors in fluid regulation (3)
- Osmoreceptors - hypothalamus, ileum
- Volume receptors - Veins, arteries, R-atrium, GIT
- Baroceptors - (failing kidney pressure)
What is the central integrator in fluid regulation
Hypothalamus
What are the effectors in fluid regulation (3)
- Hypothalamus → thirst
- ADH/AVP → less water excretion via urine
- Baroceptors → renin → angiotensin system → adrenal glands → aldosterone → less salt loss + more water retention
What are trophic changes
abnormalities in tissues, skin, or nails, often related to pain or nerve damage
What is the central integrator for trophic change regulation
Hypothalamus
What are the effectors of trophic change regulation (3)
- Corticotrophin-releasing hormone (CRH) → pituitary → corticotrophin (ACTH) → adrenal growth → cortisol
- Thyroid-releasing hormone → pituitary → thyroid stimulating hormone (TSH) → thyroid hormone (TH)
- Gonadotrophin-releasing hormone → anterior pituitary → luteinising hormone (LH) to testes → testosterone
How is there feedback inhibition of trophic change regulation
Cortisol, TH and testosterone turn off adrenal, pituitary and hypothalamus
What happens when there is too much glucose in the blood (4)
- too much glucose in the blood
- beta-pancreatic cells produce insulin which enters the blood
- insulin turns glucose into glycogen to be absorbed by body cells
- Blood glucose is reduced
What happens when there is too little glucose in the blood (4)
- too little glucose in the blood
- pancreatic alpha cells produce glucagon which enters the blood
- glucagon turns glycogen to glucose to be absorbed by body cells
- blood glucose is increased
What happens to the kidney when calcium levels decrease (4)
- calcium levels decrease
- parathyroid glands release parathyroid hormones to the kidney
- kidney activates calcitriol (the hormonally active metabolite of Vitamin D) in the small intestine
- Calcium absorption in the blood increases
What happens to the bones when calcium levels decrease (4)
- calcium levels decrease
- parathyroid glands release parathyroid hormones to the bone
- osteoclasts breakdown and transfer calcium and potassium from the bone to the blood
- Calcium absorption in the blood increases
What happens when blood pressure decreases (4)
- blood pressure decreases
- angiotensinogen is released from the liver
- renin from the kidney converts angiotensinogen to angiotensin i
- angiotensin-converting enzymes (ACE) are released from the lungs converting angiotensin i to angiotensin ii
What does angiotensin ii increase (5)
- blood pressure sympathetic activity
- tubular Na⁺, Cl⁻ reabsorption and K⁺ excretion and H₂O retention
- tells the adrenal gland cortex to secrete aldosterone retaining H₂O
- increases blood pressure through arteriolar vasoconstriction
- tells the pituitary gland to secrete ADH, causing H₂O reabsorption at the collecting duct
