Term
| What 3 components make up the cardiovascular system? |
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Definition
1. The heart: a muscular pump that drives the flow of blood through vessels.
2. Blood vessels: conduits (‘tube’ or ‘pipe’) through which the blood flows.
3. Blood: a fluid (connective tissue) medium that circulates around the body, carrying materials to and from the cells. |
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Term
| What functions, other than being a pump, does the heart perform? |
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Definition
| it performs sensory and endocrine functions that help regulate cardiovascular variables such as blood volume and pressure. |
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Term
| What functions, other than carrying blood, do the vessels perform? |
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Definition
| important sensory and effector organs that regulate blood pressure and the distribution of blood to various parts of the body |
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Term
| What is total blood flow (CO) at rest? |
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Definition
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Term
| What percentage of systemic blood does the brain receive? |
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Definition
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Term
| What percentage of systemic blood does the heart receive? |
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Definition
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Term
| What percentage of systemic blood does the muscle receive? |
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Definition
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Term
| What percentage of systemic blood does the skin receive? |
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Definition
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Term
| What percentage of systemic blood does the kidney receive? |
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Definition
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Term
| What percentage of systemic blood do the abnormal organs receive? |
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Definition
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Term
| What percentage of systemic blood do the other organs receive? |
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Definition
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Term
| Do organ size/criticality correlate to total cardiac output they receive? give an example |
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Definition
No
- kidney receives the same amount of CO as muscles do but the muscles are much larger
- kidneys receive 5x the amount the heart does |
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Term
| What do the veins and arteries do in the coronary circulation? |
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Definition
• The arteries deliver O2-rich blood to the myocardium.
• The veins remove deoxygenated blood from the heart. |
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Term
| Where do the coronary arteries branch from? |
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Definition
| The coronary arteries branch from the base of the aorta, just superior to the semilunar valve into right and left coronary arteries. |
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Term
| What does the right coronary artery branch into? |
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Definition
| the posterior descending artery (a.k.a. posterior interventricular artery) and the right marginal artery. |
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Term
| What does the left coronary artery branch into? |
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Definition
| and the left anterior descending artery (LAD) a.k.a. the anterior interventricular artery. The left marginal artery is a branch off the left circumflex artery. All these names are derived from looking at the heart ventrally. Marginal arteries lie marginally, i.e. close to the edge (just like margins do). Think about ways to remember them. |
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Term
| What coronary veins are there? |
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Definition
| The coronary veins essentially mimic the positions of the coronary arteries. There are the small, middle, great and anterior cardiac veins. |
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Term
| Describe coronary vein drainage |
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Definition
| The coronary veins converge and drain into the coronary sinus, which in turn drains directly into the right atrium, thus deoxygenated blood is returned to the heart ready to enter the pulmonary circulation (again). |
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Term
| What structural adaptations does the heart undergo? |
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Definition
- myocardium has a much greater capillary density than regular skeletal muscle
- myocardial capillary density is very high (around one capillary per myocyte cf. skeletal muscle where there is around one capillary per 20 myocytes)
- small myocyte diameter (small max diffusion distance of 9μm) |
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Term
| How else is o2 transport enhanced? |
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Definition
| presence of myoglobin in cardiac myocytes |
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Term
| How does the hearts basal blood flow compare to the rest of the body? |
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Definition
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Term
| How much oxygen does the cardiac muscle extract from the arterial blood? |
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Definition
| extracts 65-75% of the O2 from the arterial blood cf. a general body average of 25% extraction |
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Term
| Define metabolic hyperaemia |
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Definition
| the higher O2 demand during exercise is met by increased blood flow (metabolic autoregulation) |
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Term
| Describe some factors that can lead to metabolic autoregulation |
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Definition
| Possible metabolic vasodilators are interstitial hypoxia and adenosine, of which the latter is released from myocytes following ATP breakdown. |
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Term
| What stimulation leads to increased coronary blood flow? |
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Definition
Stimulation in sympathetic nerves also causes in increase in coronary blood flow. Increased sympathetic stimulation causes increased stimulation of the SA node, which fires more action potential and as a result causes an increase in contraction rate of the myocardium, which is the increase in heart rate.
Since heart rate ∝ cardiac output (CO = HR x SV) an increase in heart rate leads directly to an increase in cardiac output. |
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Term
| Describe the coronary arteries during the stages of a heart beat |
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Definition
1. compressed during systole particularly during the isovolumetric phase when the pressure within the ventricle wall can reach a whopping 240mmHg!
2. A modest flow is restored during the ejection phase of systole, but it only returns to maximum during diastole. |
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Term
| What does sudden obstruction of a coronary artery or one of its branches cause? |
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Definition
| ischaemia of the tissue downstream, leading to myocardial infarction (heart attack) |
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Term
| What does gradual obstruction of a coronary artery or one of its branches cause? |
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Definition
- development of collateral vessels, reducing the extent of the ischaemia
- however, at times of increased demand, e.g. exercise or stress, local ischaemia develops, producing the pain of angina pectoris |
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Term
| Describe capillary density in the alveolar vascular beds |
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Definition
very high
capillary surface area of up to a ginormous 100m2 |
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Term
| What causes the very high o2 diffusion capacity in the pulmonary capillaries? |
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Definition
| very small diffusion distance from the alveolar surface to the blood plasma |
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Term
| Describe the relationship between pulmonary blood flow and rate of o2 uptake by the lungs |
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Definition
| The higher the velocity of pulmonary blood flow, the faster the rate of O2 uptake by the lungs. |
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Term
| Why are pulmonary circulation pressures lower than systemic circulation pressures? |
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Definition
1. Pulmonary circulation only supplies one organ, which is effectively at, or close to, heart level, so high arterial pressures are not needed.
2. Pulmonary capillaries are not surrounded by supporting tissue and are more susceptible to stress failure (rupture) than are systemic capillaries.
3. The blood also doesn’t have to travel as far, as the lungs are only a short distance from the heart, as opposed to the systemic circulation, which pumps much further e.g. the feet etc. |
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Term
| Describe blood flow distribution in the lung of an upright subject |
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Definition
Blood flow is unevenly distributed in the lung of an upright subject because pulmonary pressure is higher at the base than it is at the apex of each lung.
At the base, the high pressure distends (‘enlarges’ or ‘balloons’) the vessels of the microcirculation, lowering their resistance and increasing flow. At the apex, the vessels actually collapse during diastole. |
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Term
| Describe the relationship between ventilation rate and the required perfusion rate |
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Definition
| The higher the ventilation rate, the higher the required perfusion rate through the lungs in order to exchange as much O2, nutrients and waste products between the alveoli and the capillaries as possible. This blood will then flow into the pulmonary veins and back to the heart, where it will be pumped around the systemic circulation. |
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Term
| How does total blood flow/CO change during exercise? |
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Definition
| Change in total blood flow/cardiac output increases from 5.8L.min-1 to around 17.5L.min-1 |
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Term
| How does brain blood flow change during exercise? |
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Definition
| Brain blood flow (750mL.min-1) remains constant, as you are not necessarily ‘using’ your brain drastically more during exercise |
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Term
| How does skeletal muscle blood flow change during exercise? |
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Definition
| increases to around 10 times (or more) its original rate |
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Term
| What is the primary determinant of systemic vascular resistance during exercise and why? |
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Definition
| Skeletal muscle resistance becomes the primary determinant of systemic vascular resistance during exercise, since most of the cardiac output will be going to the skeletal muscles (70%) |
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Term
| How much can skeletal blood flow increase? |
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Definition
| Blood flow can increase more than 10-fold with maximal vasodilation. |
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Term
| How do fast twitch and slow twitch skeletal muscle capillary density compare? |
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Definition
- greater in slow twitch than fast twitch
- slow-twitch muscle fibres have a sustained activation period
- fast-twitch muscle fibres are only active for short periods and quickly become fatigued |
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Term
| What else causes skeletal muscle blood flow to increase? |
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Definition
- skeletal muscle contractions facilitate movement of blood through veins (skeletal muscle pump)
- During skeletal muscle activity, active hyperaemia leads to an increase in blood flow. |
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Term
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Definition
| an ‘increase in blood flow associated with an increase in metabolic activity’ |
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Term
| Describe the mechanism of active hyperaemia |
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Definition
1. increased skeletal metabolism leads to local changes, which induce vasodilation e.g. reduced O2 levels and increased adenosine, K+, CO2, H+, and NO levels.
2. During exercise, these local metabolic factors primarily underlie vasodilation and overcome basal sympathetic vasoconstrictor influences.
3. During exercise, sympathetic neural activity results in vasoconstriction in other areas of the body, e.g. digestive viscera, leading to an increase in skeletal muscle blood flow. |
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Term
| Define cerebral blood flow |
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Definition
| The amount of blood that the cerebral circulation carries, which is usually around 750mL.min-1; 13% of total cardiac output. Most of this supplies the grey matter, which needs a secure O2 supply. Local supply must be adjusted to meet demand. |
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Term
| What arteries enter the cerebral circulation? |
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Definition
| the basilar and carotid arteries) anastomose to form the circle of Willis, an arrangement that helps to preserve cerebral perfusion even if one artery is occluded. |
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Term
| Describe blood flow of grey matter |
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Definition
| Grey matter has a high basal blood flow (10 times the body average) and extracts more of the O2 from the arterial blood (35% cf. a general body average of 25%). |
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Term
| How is cerebral blood flow regulated? |
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Definition
| • The brain is in the unique position of being able to regulate its own blood supply by controlling systemic cardiovascular parameters via the autonomic nervous system: perfusion of all peripheral organs (except the heart) will be sacrificed to preserve cerebral perfusion if necessary. |
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Term
| Describe cerebral autoregulation |
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Definition
| Cerebral autoregulation is highly developed (although it fails at arterial pressures below 50mmHg). Cerebral autoregulation is a combination of myogenic and local metabolic mechanisms. |
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Term
| How do cerebral blood vessels respond to arterial co2 levels? |
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Definition
• Hypercapnia causes vasodilation.
• Hypocapnia results in vasoconstriction.
Local hypoxia initiates a local vasodilation. Some of these responses may be mediated via regulation of endothelial NO production. |
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Term
| How is control of cerebral blood flow (CBF) considered? |
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Definition
| considered in terms of the factors affecting cerebral perfusion pressure (CPP) and the factors affecting cardiovascular resistance (CVR) |
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Term
| What is cardiovascular resistance (CVR) controlled by? |
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Definition
1. Metabolic control (or 'metabolic autoregulation').
2. Pressure autoregulation.
3. Chemical control (by arterial Pco2 and Po2).
4. Neural control. |
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Term
| Why does one become dizzy if one hyperventilates? |
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Definition
| Hyperventilation occurs when the rate and quantity of alveolar ventilation of CO2 exceeds the body's production of CO2. This causes the concentration of CO2 in the blood stream to fall and produces a state known as hypocapnia. The body normally attempts to compensate for this metabolically. If excess ventilation cannot be compensated metabolically, it will lead to a rise in blood pH. This rise in blood pH is known as respiratory alkalosis. When hyperventilation leads to respiratory alkalosis, it may cause a number of physical symptoms of which dizziness and headache are included. |
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Term
| Why specifically does one feel dizzy? |
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Definition
| hypocapnia causes vasoconstriction of cerebral blood vessels. |
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Term
| State the equation for cerebral blood flow |
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Definition
| cerebral perfusion pressure (CPP) / cardiovascular resistance (CVR) |
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Term
| What happens when CVR increases (because of vasoconstriction for instance)? |
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Definition
CBF decreases
then perfusion rate decreases and this means grey matter isn not supplied with blood adequately
It is this inadequate blood supply that leads to the sensation of dizziness (and/or headache). |
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Term
| What effect does shining a light onto ones retina cause? |
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Definition
a rise in temperature in the corresponding occipital lobe: an early clue that local neuronal activation may evoke a local increase in blood flow. This local ‘cortical metabolic hyperaemia’ is partially due to increases in interstitial [K+] due to outward currents from the active neurones.
Other factors may include a rise in the interstitial [H+] i.e. acidosis, and adenosine. |
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Term
| What must cerebral neurones be protected from and how? |
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Definition
| the fluctuations in the levels of ions such as Na+ and K+ that occur in the arterial blood: this is achieved by the BBB |
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Term
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Definition
| This is a physical barrier that exists between the blood and CSF (the CSF is the interstitial fluid in the CNS). The blood brain barrier blocks transcytosis and restricts the movement of hydrophilic molecules across its capillary walls |
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Term
| How does gravity influence cerebral blood flow? what is therefore needed? |
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Definition
| • Gravity influences cerebral blood flow, both directly and indirectly, due to the decreases in central venous pressure and stroke volume seen during postural hypotension. Therefore, rapid autonomic responses are needed to prevent cerebral ischaemia. |
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Term
| How does increased intracranial pressure (ICP) cause decreased blood perfusion of brain cells? |
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Definition
1. Increased ICP constitutes an increased interstitial hydrostatic pressure that, in turn, causes a decreased driving force for capillary filtration from intracerebral blood vessels.
2. Increased ICP compresses cerebral arteries, causing increased cerebrovascular resistance. |
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Term
| What are the 3 main functions of cutaneous blood flow? |
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Definition
1. Heat exchange for thermoregulation.
2. Supply of nutrients to the skin cells.
3. Blood reservoir. |
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Term
| What are venous plexuses? |
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Definition
- extensive networks under skin surface.
- flow can range from 50-2500mL.min-1 depending on body temperature. |
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Term
| What does cutaneous blood flow reflect? |
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Definition
| neural adjustments of blood flow through arterioles and coiled arteriovenous anastomoses. These arteriovenous ‘shunts’ are mainly located in the fingertips, palms of hands, toes, feet, ears, nose and lips. |
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Term
| What are arteriovenous shunts richly supplied with? |
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Definition
- sympathetic nerve endings
- shunts are under the control of reflexes, linked to temperature receptors or signals from higher CNS centres (hypothalamus). |
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Term
| What is the response to heat? |
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Definition
• Hypothalamus signals reduced vasomotor tone i.e. vasodilation, leading to increased blood flow.
• Substances in sweat lead to production of bradykinin, which stimulates endothelial cells to release NO, leading to further vasodilation.
• Vasodilation means that the blood runs closer to the dermis, thus radiating heat (losing heat) from the body.
• Sweat also increases the latent heat radiated from the body as it evaporates, as in the latent heat of vaporisation. |
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Term
| What is the response to cold? |
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Definition
• Superficial vessels constrict strongly.
• Blood bypasses capillaries, via arteriovenous shunts, diverting blood to vital organs.
• Sometimes, skin may appear paradoxically ‘rosy’, when cold. This occurs because blood can become trapped in superficial capillary loops following rapid vasoconstriction, and because skin uses less O2 when cold. |
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Term
| What effect does alcohol have? |
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Definition
| Alcohol causes dilation of blood vessels within the skin, resulting in a flushed appearance, increased sweating and heat loss. Blood flow to muscle changes little or may decrease. |
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Term
| What can alcohol contribute to? |
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Definition
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