3 Blood Pressure Flashcards
What are 3 different capillary types?
Continuous
Fenestrated
Sinusoid
Where are continuous capillaries found?
Continuous capillaries are the most common type of capillaries found in tissues such as muscles, skin, lungs, and the central nervous system. Their role is to facilitate the exchange of gases, nutrients, and waste products between the blood and surrounding tissues. These capillaries have a continuous endothelial lining with tight junctions between cells, limiting the passage of large molecules while allowing smaller ones, like water, ions, and glucose, to pass through via diffusion. The tight junctions help maintain blood-brain barrier integrity in the brain and regulate the selective permeability in other tissues.
Where are fenestrated capillaries found?
Fenestrated capillaries are specialized capillaries found in organs that require rapid exchange of larger volumes of substances, such as the kidneys, intestines, and endocrine glands. These capillaries have endothelial cells with small pores (fenestrae) that allow for the passage of larger molecules like hormones, nutrients, and waste products, as well as water, while still maintaining some level of selectivity. In the kidneys, for example, fenestrated capillaries are involved in filtration, allowing for the rapid removal of waste from the blood. In the intestines and endocrine glands, they facilitate nutrient absorption and hormone secretion.
Where are sinusoid capillaries found?
Sinusoid capillaries are specialized, wide, and irregularly shaped capillaries that allow for the free exchange of large molecules and even cells between the blood and surrounding tissues. They are found in organs involved in the production and filtering of blood, such as the liver, spleen, and bone marrow.
The endothelial lining of sinusoid capillaries is discontinuous, with large gaps that permit the movement of larger substances, including blood cells and proteins, in and out of the bloodstream. In the liver, for example, they facilitate the exchange of nutrients, waste, and blood cells, essential for processes like detoxification and blood cell formation.
What does flow depend on?
Pressure difference
Resistance of the vessel
What is the equation of Ohm’s Law and purpose?
Calculate Flow (Q)
Q = ( Pressure at beginning - Pressure at end of vessel ) / Resistance
What is Poiseulle-Hagen Formula and its purpose?
Calculate resistance
R = ( 8 x viscosity x Length ) / pi x r^4
What is the equation for mean arterial pressure?
Cardiac output x total resistance
What mainly causes total peripheral resistance?
Arterioles are the main site of resistance because of such a small radius
What is capacitance?
Capacitance refers to the ability of blood vessels, particularly veins, to expand and hold a large volume of blood without a significant increase in pressure.
Veins are considered “capacitance vessels” because they store blood and help regulate blood volume distribution in the body.
The high compliance of veins allows them to accommodate large changes in blood volume with minimal changes in pressure.
This property plays a key role in maintaining cardiovascular stability, especially during changes in body posture or blood volume.
How is capacitance reduced?
Contraction of veins reduces capacitance
Blood volume in arterioles is small, so constriction does not change capacitance much
What affects total peripheral resistance the most?
Constriction of arterioles increases total peripheral resistance
Resistance in veins is small, so venoconstriction does not change TPR much
Explain capillary exchange
Explain the lymphatic circulation
Name 4 causes of oedema
Increase in venous pressure
Decrease in oncotic pressure
Decrease in lymphatic flow
Increase capillary permeability
What does diurnal variation of blood pressure mean?
Refers to the natural fluctuations in blood pressure that occur throughout the day and night.
Typically, blood pressure is lower during sleep and rises in the morning upon waking, reaching its peak during midday and late afternoon.
These variations are influenced by factors like the body’s circadian rhythm, physical activity, stress levels, and hormone release.
Why does blood pressure drop upon standing? ***
Gravity
Compliance of veins
How does the body sense acute change in blood pressure?
Arterial baroreceptors
What is the short-term regulation of blood pressure?
Autonomic regulation (lasts mins to days)
Decreased parasympathetic efferent output affects SA node
Increase HR to increase CO
Blood pressure is now increased and restored
What is the long-term regulation of blood pressure?
Volume regulation = fluid absorption by the kidneys
Major compensation of cardiac failure (inadequate CO)
Why is controlling blood flow necessary?
Each tissue receives only a fraction of total CO
Increasing CO increases work done by the heart to pump blood
Each tissue must receive sufficient blood flow for its metabolic needs, otherwise necrosis will occur
How is blood flow controlled?
Controlling tissue perfusion, so each tissue receives just enough blood while CO and heart work are MINIMISED
Arteriolar resistance determines the perfusion through an organ
Resistance of parallel systemic vascular beds determines the distribution of blood flow through organs
What is active hyperaemia?
Increased metabolic rate increases blood flow
Hyperaemia = increased blood flow
What are the metabolic mediators?
O2 - CO2 - H+
K+ - PO43-
Glucose
Adenosine
What metabolic mediators have a VASODILATORY effect when increase at TISSUE level?
CO2 (except pulmonary)
H+
K+ (in low doses)
PO43-
Adenosine
What metabolic mediators have a VASOCONSTRICTION effect when increase at TISSUE level?
O2 (except pulmonary)
Glucose
Describe the blood flow in skeletal muscles
Low at rest, increase during exercise
At rest, arterioles and flow = controlled by sympathetic nerves
Strong response to active hyperaemia
During activity, flow controlled by local metabolites
Active muscles get increased blood flow, inactive muscles get less blood flow
Describe the blood flow in coronary blood flow
Blood flow reduced in systole
Greater flow in DIASTOLE
Blood flow through heart is controlled by active hyperaemia (little response to sympathetic nerves or hormones)
Adenosine is important metabolite for coronary flow
Describe the cerebral blood flow
Control is by autoregulation = almost constant from 60-160mmHg
Increased blood flow when you think
Responds well to metabolites but not sympathetic nerves or hormones
Describe the blood flow in the skin
At rest in normal room temp = skin receives more blood flow than needed for metabolism
Skin blood flow depends on TEMP
Blood transports heat to skin and cool blood returns
Heat exhaustion = CO needs to increase to provide more blood to exercising muscles
Also needs to increase dilation so blood flow goes to skin to RELEASE HEAT
What is pulmonary blood pressure?
22/8mmHg
