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By the end of this section, you will be able to:
  • Identify the primary mechanisms of capillary exchange
  • Distinguish between capillary hydrostatic pressure and blood colloid osmotic pressure, explaining the contribution of each to net filtration pressure
  • Compare filtration and reabsorption
  • Explain the fate of fluid that is not reabsorbed from the tissues into the vascular capillaries

The primary purpose of the cardiovascular system is to circulate gases, nutrients, wastes, and other substances to and from the cells of the body. Small molecules, such as gases, lipids, and lipid-soluble molecules, can diffuse directly through the membranes of the endothelial cells of the capillary wall. Glucose, amino acids, and ions—including sodium, potassium, calcium, and chloride—use transporters to move through specific channels in the membrane by facilitated diffusion. Glucose, ions, and larger molecules may also leave the blood through intercellular clefts. Larger molecules can pass through the pores of fenestrated capillaries, and even large plasma proteins can pass through the great gaps in the sinusoids. Some large proteins in blood plasma can move into and out of the endothelial cells packaged within vesicles by endocytosis and exocytosis. Water moves by osmosis.

Bulk flow

The mass movement of fluids into and out of capillary beds requires a transport mechanism far more efficient than mere diffusion. This movement, often referred to as bulk flow, involves two pressure-driven mechanisms: Volumes of fluid move from an area of higher pressure in a capillary bed to an area of lower pressure in the tissues via filtration    . In contrast, the movement of fluid from an area of higher pressure in the tissues into an area of lower pressure in the capillaries is reabsorption    . Two types of pressure interact to drive each of these movements: hydrostatic pressure and osmotic pressure.

Hydrostatic pressure

The primary force driving fluid transport between the capillaries and tissues is hydrostatic pressure, which can be defined as the pressure of any fluid enclosed in a space. Blood hydrostatic pressure is the force exerted by the blood confined within blood vessels or heart chambers. Even more specifically, the pressure exerted by blood against the wall of a capillary is called capillary hydrostatic pressure (CHP)    , and is the same as capillary blood pressure. CHP is the force that drives fluid out of capillaries and into the tissues.

As fluid exits a capillary and moves into tissues, the hydrostatic pressure in the interstitial fluid correspondingly rises. This opposing hydrostatic pressure is called the interstitial fluid hydrostatic pressure (IFHP)    . Generally, the CHP originating from the arterial pathways is considerably higher than the IFHP, because lymphatic vessels are continually absorbing excess fluid from the tissues. Thus, fluid generally moves out of the capillary and into the interstitial fluid. This process is called filtration.

Osmotic pressure

The net pressure that drives reabsorption—the movement of fluid from the interstitial fluid back into the capillaries—is called osmotic pressure (sometimes referred to as oncotic pressure). Whereas hydrostatic pressure forces fluid out of the capillary, osmotic pressure draws fluid back in. Osmotic pressure is determined by osmotic concentration gradients, that is, the difference in the solute-to-water concentrations in the blood and tissue fluid. A region higher in solute concentration (and lower in water concentration) draws water across a semipermeable membrane from a region higher in water concentration (and lower in solute concentration).

Questions & Answers

Which of the following hormones are responsible for the adolescent growth spurt? estrogen and testosterone, even in women?
Kepa Reply
estrogen
Farhana
Estrogen!
Jazil
What is sling give d characteristics of sling uses of sling
adamu Reply
I went to learn anatomy of joints
Arman Reply
me 2
adamu
joint have 3 cartilaginous joint fibrous joint synovial joint U can reserch in Google can explain U well
sopheaktra
define sling
adamu
To throw with a circular or arcing motion
real
what is respiration
Osele Reply
what is respiration
Paul
Respiration is the process by which oxygen is taken in and carbon dioxide is given out.
Md
Respiration is the combination of inhalation and exhalation.
Khim
inhalation is the taking in air from environment to lung and exhalation is taking out sir from the lung to environment ..
Khim
what is holistic
Kibrom Reply
Holistic means encompassing the whole of a thing, and not just the part. Holistic medicine looks at the whole person for answers, not just at physical symptoms. You might have heard of holistic medicine, which tries to treat someone as mind and body, instead of treating only the part of the patient
I want to learn one by one system like skeleton system... muscular system
Mary Reply
i want to learn this
Kibrom
explain in details factors that affects bone development
Precious Reply
describe the process of bone healing
Precious
out line factors that delays bone healing
Precious
actually,for the bone formation they must be sufficient level of calcium,phosphorus and vitamin D in the body for it to happen smoothly.
lucky
the above mentioned substances are the ones able for the formation and repairing of bones.
lucky
explain in details factors that affects bone development
Precious
what are tissue
muki Reply
a lots of cells make tissue and a cell body is tissue
Rabab
cells come together to form a tissue and tissues come together to form an organ
Adoma
what is appendicular skeleton
OSE Reply
appendicular skeleton is upper limbs and lower limbs
sopheaktra
what is decompression sickness?
Japhar Reply
It occurs in Scuba divers when they rise too quicky to the sea surface , their oxygen tanks have oxygen mixed with N2 gas which has a high solubility at sea level , when the diver rises the N2 gas bubbles out of plasma and this causes Air Ebolism
Siphiwesihle
if a single part if Nervous system doesn't function like synapse? what will occur
Lilian Reply
no transmission of impulses no respond cause mechanical damage
Komolika
what happens when calcium ion channel is blocked
Jachike
a MORAH /MORAH
Kechi
meaning?
Jachike
transmission of impure
sopheaktra
when calcium ion channels block . lightheadedness Low blood pressure. Slower heart rate. Drowsiness. Constipation. Swelling of feet ankles and legs. Increased appetite. Gastroesophageal reflux disease (GERD
sopheaktra
I'm not sure about it
sopheaktra
what is this substance
Peng Reply
In the human body, there are no atoms as separate entities. Instead, they constantly interact with other atoms to form and break down more complex materials. To fully understand anatomy and physiology, you must understand how atoms are involved in such interactions. The key is to understand the beha
Warid
what are functions of muscle cell
Veronicah
please can someone help with ten functions of the following hormones 1.Gastrin 2. Adrenal sex hormone 3. Secretin 4. Follicle Stimulating Hormone 5. Glucagon 6. Progesterone
Har
4.produces the oetrogen and bursts open to release egg cells.
Komolika
5.regulates the level of glucose in the blood and it is secreted when glucose low in the blood.
Komolika
many layers that are covering the heart
Komolika Reply
number and names of covering layers of the heart, 🙏
Komolika
what is oogenesis
okolie Reply
formation of an egg cell
Japhar
yeah
Tahir
ok
okolie
the reproduction of egg cells
Komolika
what is evolution
Muritala Reply
?
Kashif

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Source:  OpenStax, Anatomy & Physiology. OpenStax CNX. Feb 04, 2016 Download for free at http://legacy.cnx.org/content/col11496/1.8
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