Intro 1 Flashcards
What factors affect diffusion?
-Area available for exchange. Determined by the Capillary Density (Capillaries per unit volume). This varies from tissue to tissue and is highest in those that are most metabolically active.
. -Diffusion Resistance – The difficulty of movement through the barrier. The nature of the barrier and the molecules that are diffusing. A major component of diffusion resistance is the distance over which diffusion must occur, the path length.
-Concentration gradient. Concentration gradients drive diffusion, the relevant gradient being between the capillary contents and the nearby cells. This gradient does depend on the concentration of substances in the blood, but the more important variable is the flow of blood through the capillary. Unless blood is supplied at an appropriate rate, the gradients driving exchange will dissipate.
What is perfusion rate?
Rate of blood flow to a tissue
What is the perfusion rate to the brain?
0.75 L/min to the brain at all times
What is the perfusion rate to the heart?
0.9 to 3.6ml.min-1g-1
What is the perfusion rate to the kidneys?
3.5ml.min-1g-1
How is blood distributed in the body?
5 litres overall roughly.
- 11% (0.55 L) in the Arteries and Arterioles
- 5% (0.25 L) in the Capillaries
- 17% (0.85 L) in the Heart and Lungs
- 67% (3.35 L) in the Veins
What are Venae Comitantes
These are the deep paired veins that, in certain anatomical positions, accompany one of the smaller arteries on each side of the artery. The three vessels are wrapped together in one sheath. The pulsing of the artery promotes venous return within the adjacent, parallel, paired veins. Examples are the brachial, ulnar and tibial venae comitantes.
What is systole?
Left ventricle contraction causes the blood pressure in the aorta to rise to approx 120mmHg (systolic pressure). The walls of the elastic aorta (and other elastic arteries) stretch.
What is diastole?
The aortic semilunar valve closes. The walls of the aorta recoil, maintaining pressure on the blood and moving it towards the smaller vessels. Aortic pressure drops to 70–80mmHg (diastolic pressure).
What are the three layers of the pericardium?
Fibrous Pericardium - the outer fibrous sac that covers the heart.
Parietal Pericardium - lies between the visceral pericardium and the fibrous pericardium.
Visceral Pericardium - also called the epicardium, this is the outer layer of the wall of the heart.
What is the function of the pericardium?
-Keeps the heart contained in the chest cavity.
-Prevents the heart from overextending when blood volume increases.
-Limits heart motion.
-Pericardial fluid lubricates heart, preventing damage from friction
What is pericarditis?
Pericarditis is swelling of the pericardium, which is the fluid-filled sac surrounding your heart. In rare cases, pericarditis can trigger a serious complication known as cardiac tamponade. This is an excess build-up of fluid inside the pericardium. The extra fluid places too much pressure on the heart, so it is unable to beat properly.
Cardiac tamponade can cause symptoms such as:
- light-headedness
- blurred vision
- palpitations
- nausea
Cardiac tamponade also often occurs alongside inflammation of the heart muscle (myocarditis). This causes pain that feels like pressure on the chest, similar to a heart attack.
What is the difference between serum and plasma?
Serum= plasma - clotting factors, especially fibrinogen
Plasma is the fluid collected from unclotted blood.
What is the commonest cause of marked increase in whole blood viscosity?
- Multiple Myeloma
- Note that increased temperature means lower viscosity
Note that increased viscosity can lead to sludging of blood in peripheries
What factors can cause minor changes in blood viscosity?
-raised levels of acute phase plasma proteins, such as fibrinogen, complement factors and CRP
