Homeostasis

Front 1

Give some examples of physiological variables maintained by Homeostasis.

Back 1

Core temperature, Water & electrolyte concentrations, pH, Blood glucose levels, blood and tissue oxygen and carbon dioxide levels, blood pressure.

Front 2

The body can regulate its internal environment through many feedback systems or loops; what are three basic components of a feedback system?

Back 2

Receptor – monitors change and sends input (afferent pathway), nerve impulse or chemical signal, to Control centre which evaluates input received and generates commands (efferent pathway), nerve impulse or chemical signal, to the Effector which produces a response that changes the controlled condition.

Front 3

Is the control of blood pressure maintained by a positive or negative feedback? Briefly describe the process and the hormones involved when blood pressure drops.

Back 3

Negative feedback. RAAS – Baroreceptors in the juxtaglomerula apparatus in the renal corpuscle detect a drop in BP and release renin. This metabolises angiotensinogen (from liver) to angiotensin 1 which is further metabolised in the prescence of angiotensin converting enzyme (ACE, from lungs) to angiotensin 2.

Angiotensin 2 is a potent vasoconstrictor and also stimulates the adrenal glands to increase the release of aldosterone which increases the reabsorption of sodium in the collecting ducts and therefore water from urine into the blood, increasing blood volume.

Front 4

Levels of which hormone are controlled by positive feedback?

a) growth hormone

b) thyroid stimulating hormone

c) oxytocin

d) insulin

Back 4

Oxytocin

Synthesised by hypothalamus and secreted from posterior pituitary gland, oxytocin stimulates contraction of smooth muscle in the uterus which in turn stimulates the synthesis and secretion of more oxytocin increasing frequency and force of more contractions. This positive feedback loop terminates with birth.

Front 5

nervous control of HR

Back 5

Internal carotid artery and aortic arch. Send signals to medulla where cardiac control centre is located. Aortic arch via vagus nerve, carotid via glossy pharyngeal nerve.

BP too high -parasympathetic fibres of vagus nerve slows SA node by releasing ACh.

BP too high - sympathetic fibres of cardiac nerve releasing nor adrenaline at SA node to increase HR

Front 6

Clotting (haemostasis)

Back 6

Endothelial damage exposes collagen in endothelial walls. Platelets stick to collagen, platelets then release thromboxane A2 to call more platelets to injury site.

Platelets aka thrombocytes.

Tissue factor is also released due to damage of the endothelium which initiates the extrinsic clotting pathway eventually leading to fibrin formation.

Fibrin then starts to make a mesh to trap RBCs.

Front 7

Cox inhibitors

Back 7

Cox converts arachodonic acid to prostaglandins which in turn is converted to thromboxane.

Cox inhibitors such as aspirin inhibit cox and therefore reduce prostaglandin and thromboxane production.

Front 8

Coag cascade

Back 8

Intrinsic pathway - amplifies the cascade

Extrinsic pathway - most important in initiation of pathway. Starts due to tissue factor from damaged tissue being released.

Both pathways converge so that factor 10a convert prothrombin to thrombin. Thrombin then converts fibrinogen to fibrin.

Thrombin has a role to play in positive feedback on many of the extrinsic pathway clotting factors leading to fibrin++ in a short amount of time.

Front 9

Anti coags

Back 9

Anti thrombin 3 is an indirect factor 10 and inhibitor occurring naturally. Heparin enhances anti thrombin 3.

Rivaroxaban / apixaban is a direct inhibitor of factor Xa

Plasminogen converts to plasmin which breaks down fibrin mesh naturally. Reteplase/ tenectaplase bind with plasminogen to convert it to plasmin and therefore enhances fibrin mesh breakdown.

Warfarin is a bit k reductase inhibitor. This prevents bit k reductase been made which is important in the manufacture of factors 2,7,9,10 from glutamic acid.

Front 10

Intrinsic/extrinsic pathway

Back 10

Front 11

Anti coags

Back 11

Front 12

Anti platelets

Back 12

Aspirin via cox inhibition

Clopidigrel via binding to P2Y on platelet, blocking adp induced platelet aggregation.

Front 13

Blood

Back 13

A connective tissue.

RBCs (45%)

WBCs (aka leukocytes)

Platelets(thrombocytes)

Plasma (55%)

Front 14

Plasma make up

Back 14

90%water

Solutes such as sodium and potassium

Plasma proteins such as albumin

Front 15

Chemoreceptors

Back 15

Monitor, oxygen, carbon dioxide and pH. Found in the respiratory centre of the medulla, carotid and aortic bodies.

Front 16

Bp and cardiac output

Back 16

BP = cardiac output x peripheral resistance

Cardiac output =stroke volume x HR

Front 17

Controlling temperature

Back 17

Thermoeegulatory centre in hypothalamus.

Works by altering metabolic rate via adrenaline and thyroid, causes vasodilation/constriction and control of sweat glands

Underdeveloped in young children

Front 18

Temperature and oxygen dissociation curve

Back 18

High temp is rightward shift, lower affinity for O2, will give it away to tissues easier as there is greater demand.

Hypothermia, leftward shift, holds on to oxygen more, less demand from tissues.

Front 19

INR

Back 19

Prothrombin time

0.8-1.1 normal, more than this = slower to clot

2.0-3.0 normal for those on warfarin

Front 20

Haematocrit

Back 20

Proportion of blood made up of cells.