Capillary Exchange

Question 1

What is capillary exchange?

Answer 1

Movement of substances between blood and interstitial fluid

Question 2

What are the basic mechanisms that control the exchange of nutrients?

Answer 2

Diffusion, osmosis

Question 3

What is the most important method of capillary exchange?

Answer 3

Simple diffusion

Question 4

Which substances enter and leave capillaries by simple diffusion?

Answer 4

O2, CO2, glucose, amino acids, and hormones

Question 5

Why does O2 diffuse from blood to tissues?

Answer 5

Because O2 has a higher concentration in the blood than in the tissues.

Question 6

What happens to CO2 during capillary exchange?

Answer 6

CO2 diffuses from tissues into the blood.

Question 7

What is Blood Hydrostatic Pressure (BHP)?

Answer 7

BHP is simply the water pressure inside your blood vessels, specifically the tiny ones called capillaries

Question 8

hydrostatic pressure…

Answer 8

pushes fluid

Question 9

osmotic pressure…

Answer 9

pulls fluid

Question 10

What does BHP (Blood Hydrostatic Pressure) do in the context of capillaries?

Answer 10

BHP pushes fluid out of the capillaries into interstitial fluid.

Question 11

Blood osmotic pressure…

Answer 11

Blood osmotic pressure
“Pulls” fluid from interstitial spaces into capillaries

Question 12

Colloid osmotic pressure…

Answer 12

osmotic pressure of solutes
pulling water in from the interstitial space

Question 13

Interstitial fluid osmotic pressure (IFOP)

Answer 13

Osmotic pressure in the interstitial space pulling water from the blood vessel

Question 14

Net Filtration Pressure (NFP)

Answer 14

Balance of bulk flow pressures (push and pull)

Question 15

Net Filtration Pressure

Answer 15

Indicates the direction of fluid movement (net out vs net in)

Question 16

Which substances enter capillaries by simple diffusion?

Answer 16

CO2 and wastes

Question 17

The lymphatic system has three main functions:

Answer 17

1. Lymphatic capillaries take up excess tissue fluid and return it to the bloodstream.
2. Lymphatic capillaries absorb fats from the digestive tract and transport them to the bloodstream (lacteals).
3. Helps defend the body against disease.

Question 18

When lymphatic capillaries take up excess tissue fluid it becomes…

Answer 18

lymph

Question 19

Physicians often feel for the presence of swollen, tender lymph nodes as evidence that the body…

Answer 19

…is fighting an infection

Question 20

Umbilical Arteries: Fetal function

Answer 20

Fetal Function: Carries deoxygenated blood and wastes from the fetus to the placenta.

Question 21

adult remnant: Umbilical arteries

Answer 21

Medial Umbilical Ligaments (fibrous cords on the abdominal wall).

Question 22

Umbilical Vein: Fetal function

Answer 22

Carries oxygenated, nutrient-rich blood from the placenta to the fetal liver/ductus venosus.

Question 23

adult remnant: Umbilical Vein

Answer 23

Ligamentum Teres (or Round Ligament of the Liver).

Question 24

Ductus Venosus: Fetal function

Answer 24

Bypasses the non-functional fetal liver by shunting blood from the umbilical vein directly to the Inferior Vena Cava (IVC).

Question 25

adult remnant: Ductus Venosus

Answer 25

Ligamentum Venosum.

Question 26

Foramen Ovale: Fetal function

Answer 26

Fetal Function: Shunts blood from the Right Atrium to the Left Atrium, bypassing the fetal lungs (most blood bypasses).

Question 27

adult remnant: Foramen Ovale

Answer 27

Fossa Ovalis (a slight depression in the interatrial septum).

Question 28

Ductus Arteriosus: Fetal function

Answer 28

Fetal Function: Shunts blood from the Pulmonary Artery (after the right ventricle) to the Aorta, bypassing the fetal lungs (the rest of the blood bypasses).

Question 29

What is the main force that drives fluid OUT of the capillary and into the interstitial space?

Answer 29

Blood Hydrostatic Pressure (BHP) (or Blood Pressure). It is strongest at the arteriole end of the capillary, physically pushing fluids, solutes, and gases out of the vessel.

Question 30

Adult Remnant: Ductus Arteriosus

Answer 30

Ligamentum Arteriosum.

Question 31

What is the main force that drives fluid INTO the capillary from the interstitial space?

Answer 31

Blood Colloid Osmotic Pressure (BCOP). This pressure is created by solutes, specifically plasma proteins (like albumin) that are too large to leave the blood. Water is drawn back into the capillary due to osmosis.

Question 32

Explain the fluid exchange process at the Arteriole End (front) of the capillary.

Answer 32

OUTWARD Movement: BHP (35 mmHg) > BCOP (25 mmHg). The net pressure is outward, driving filtration. Fluids, small solutes, O2, and nutrients move out to the tissues.

Question 33

Explain the fluid exchange process at the Venule End (back) of the capillary.

Answer 33

INWARD Movement: BHP (17 mmHg) < BCOP (25 mmHg). The BCOP remains constant, but BHP drops. The net pressure is inward, driving reabsorption. Fluids, CO2, and metabolic wastes move in from the tissues.

Question 34

What happens to the remaining ∼10-15% of filtered fluid not reabsorbed at the venule end?

Answer 34

It is picked up by the Lymphatic System. This fluid (now called lymph) is filtered, cleaned, and eventually returned to the venous circulation near the heart.