Download Lecture 12: Blood and Capillary Exchange

Lecture 12: Blood and Capillary Exchange
Silverthorn Chapter 16
The 70 kg man has 5 L of blood (this is about 10.5 pints). Blood consists of several different parts:
1. Plasma: Fluid portion of blood (3 L)
A. 92% water, 7 % plasma proteins
B. 1 % other dissolved stuff (AA, glucose, lipid, O2, vitamins, etc)
C. Identical to interstitial fluid, except for plasma proteins
i. Increases the osmotic pressure in the blood, drawing water from the interstitial fluid into the blood
ii. Includes antibodies, etc…
iii. The liver makes most of the plasma proteins
2. Cellular elements: (2 L) (fig 16-2)
A. All blood cells descend from pluripotent hematopoietic (heee ma toe poe eee tic) stem cell in bone marrow…
B. RBC (erythrocytes)- respiratory system
C. WBC (leukocytes) – immune system
D. Platelets (thrombocytes) – clotting
Capillary Exchange
Your body has 50,000 miles of capillaries with a surface area equal to 2 football fields
There are several types of exchange:
1. Diffusion of stuff down concentration gradients…
2. Transcytosis (fig 5-24)
3. Bulk flow of fluid in and out of the capillaries due to pressure gradients:
A. Hydrostatic (the push of fluid thru cap pores due to the beating heart)
B. Osmotic (the pull of fluid back in b/c of plasma proteins!)
C. Figs 5-26, 15-19
i. Hydrostatic decreases due to friction
ii. # of plasma proteins stays the same, so osmotic pressure does not change
D. Filtration: net flow of fluid out of plasma into interstitial fluid
E. Absorption: net flow into the plasma from the interstitial fluid
F. Different junctions can determine leakiness…more leaky = more filtration
4. Ultimately, more fluid flows OUT than IN…About 3L filtered every day…
5. Excess fluid is deposited into the Lymphatic System
Lymphatic System
1. Fluid is pumped around super-leaky vessels and deposited back into the circulation (under the collar bones)
2. Edema(swelling due to gathering of fluid in the interstitial space) occurs when there is a problem with exchange between
circulatory system and lymphatic system. Can occur if:
A. Lymph is not draining correctly due to problems in the lymph nodes
B. Filtration exceeds absorption in the capillaries…
i. EX: Inflammation --> leaky capillary walls --> fluid is pushed out easier
EX: If starving (low protein in blood) fluid pours out of system (ascites, or \kwä-shē-ȯr’-kər)
Bio 7: Human Physiology
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Spring 2014: Riggs
Platelets facilitate clotting
Platelets are tiny little cell fragments responsible for clotting. They are also called thrombocytes.
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They are born from megakaryocytes as they splinter while squeezing into the blood stream.
Have many cell parts like a regular cell…(ER parts, golgi parts, mitochondria)
Have intracellular enzymes (and other chemicals) that promote vascular healing and other clotting events.
Also are covered in special glycoproteins that STICK TO DAMAGED TISSUE (especially endothelial cells AND exposed
collagen!)
5. Don’t live very long…half life is 8-12 days (med 458), then they are removed from the blood by the SPLEEN
Blood clotting
Upon damage to a vessel, 3 things happen…
1. Vasoconstriction
A. Immediate
B. Vessel cells surrounding the damage secrete vasoconstrictors
C. Platelets secrete thromboxane A2 (a vasoconstrictor)
2. Platelet plug formation
A. Platelet contacts damaged endothelium OR exposed collagen in vessel…
B. Platelet ACTIVATES
i. Becomes sticky…
ii. Grows in size…
iii. Becomes irregularly shaped
iv. Produce thromboxane A2, which ACTIVATES nearby platelets!
C. You end up with a platelet activation CASCADE that results in a glob of sticky platelets…the platelet plug.
D. Platelet plug formation is CRITICAL for healing the THOUSANDS of tiny ruptures in small vessels each day!
E. Someone with few platelets can lose blood b/c of these many tiny openings!
3. Blood clot formation
A. Begins within 15-20 seconds in a severe trauma, and within 1-2 minutes otherwise.
B. At any given time, there are 2 types of substances floating in the blood
i. Procoagulants (dominate at the site of damage, b/c they are activated by the damage!)
ii. Anticoagulants (dominate if no damage)
C. Generally has 3 stages:
i. A complex cascade is initiated, resulting in prothrombin activator.
a. Rate limiting step
b. This is caused by vessel damage
c. This is extremely complex…
ii. Prothrombin activator converts prothrombin into thrombin
a. Prothrombin (plasma protein) is produced in the LIVER and Vitamin K is required to create it! (low Vitamin K
leads to clotting problems)
b. Prothrombin is unstable
iii. Thrombin turns fibrinogen to fibrin fibers
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a. Fibrinogen is also produced in the liver (and is a plasma protein)
b. Fibrin fibers form a crazy mesh that eventually is a TIGHT scab.
Results in a thick meshwork of fibrin fibers and entrapped blood cells, platelets, and plasma that STICKS to the damaged
endothelium.
Clot retraction occurs within 20-60 min, where the fluid inside the clot is squeezed OUT. The fluid is SERUM…
A. Calcium found in the ER of the platelets (!) plays a huge role in the contraction of the clot!
CRAZY POSITIVE FEEDBACK CYCLE…
A. But once the clotting process is complete, the bleeding stops, the damaged tissue is covered with the clot, and the original
stimulus is removed.
The platelet plug is essentially the beginning of the clot, b/c the fibrin fibers thread through the sticky plug and solidify the whole
deal. Med 458.
Bio 7: Human Physiology
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Spring 2014: Riggs
Ext Brain 12: Blood, Capillary Exchange
STUDY GUIDE QUESTIONS:
1. Understand the 3 methods by which exchange of nutrients and wastes occurs in the capillaries.
2. Be able to explain the relationship between hydrostatic and osmotic pressure in the capillaries.
3. Define “filtration” vs. “abosorption” and know whether net filtration or absorption occurs in the capillaries every day.
4. What is the purpose of the lymphatic system?
5. What is edema?
6. Describe the composition of blood.
7. Be able to describe the anatomical differences between the various blood vessels in the body and relate these structural
differences to their functional differences.
8. What are platelets? Describe their structure and general function.
9. What are the 3 things that happen when a blood vessel is damaged?
10.What is thromboxane A2? Describe two important roles of thromboxane A2 following damage to a vessel.
11. What is the mechanism of action that explains how aspirin works?
12.Compare and contrast an activated platelet vs a non-activated platelet.
13.Why is platelet activation considered a positive feedback cycle?
14.Compare and contrast the platelet plug and a blood clot.
15.Clearly describe the 3 stages of clot formation, to the detail discussed in lecture.
16.What is the role of vitamin K in blood clot formation?
17.How does Coumadin work?
Bio 7: Human Physiology
43
Spring 2014: Riggs