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Determinants of mean arterial pressure
Transcript of Determinants of mean arterial pressure
Mean arterial pressure is the average pressure in the arteries, generated by the heart. Adequate MAP is necessary to deliver blood to within a cell's length of every cell in the body
Cardiac output (CO) = HR * SV
Increased CO leads to increased MAP
Decreased CO leads to decreased MAP
Increased blood volume causes increased MAP, and loss of blood volume reduces MAP. All body fluids are filtrates of the blood, so any loss of fluid can result in reduced MAP. Kidneys can conserve fluid or get rid of extra fluid, but external inputs are required to add back lost fluids
Determinants of mean arterial pressure (MAP)
Mean Arterial Pressure (MAP)
Total peripheral resistance
Heart rate is measured in beats per minute, and is determined by the pacemaker cells in the sinoatrial node of the heart. The SA node generates AP's at 100 bpm, but this slows down with parasympathetic input, and speeds up with sympathetic input.
MAP = CO *TPR
(Total peripheral resistance)
Blood pressure is highest as it leaves the heart, and lowest when it returns to the heart
Redistribution of blood
1. Sympathetic activation at alpha-adrenergic receptors (avert blood away)
2. Antidiuretic hormone (ADH) = vasopressin
3.Angiotensin II (ANG II)
Low MAP, high plasma osmolarity, decreased atrial stretch
increased number of AP's in baroreceptor neurons
Increased secretion of ADH(vasopressin) from the PPG
Water conservation by kidneys
Decreased renal blood pressure
Increased secretion of renin from kidney
(ACE=angiotensin converting enzyme)
Increased ADH secretion
Increased aldosterone secretion from
Increased sympathetic output
1. Increased [bad stuff] eg. CO2, H+, K+ and other organic acids - local.
2. Decreased [good stuff] eg. oxygen, glucose - local.
3. Sympathetic activation of beta-adrenergic receptors on blood vessels that supply skeletal muscle, liver, heart (bigger blood blast) -endocrine.
4. Increased atrial natriuretic peptide (ANP) endocrine.
5. Increased nitric oxide (NO) -local effect.
6. Increased [histamine] - usually a local effect
How does alcohol affect ADH?
Excess fluid ingested
causes increased blood volume
Increased atrial stretch
Increased ANP release from heart
More urine formed in kidneys.
Relaxation of vascular circular smooth muscle.
Reduced blood volume and lower MAP
Normal histamine function
When histamine effects are systemic, anaphylactic shock can occur