CV 3 (2) Flashcards
Veins have all — distinct layers (tunics). The walls are thinner than arteries, so they often appear — in histological slides.
three
collapsed
Compared to arteries, veins have (3)
less smooth muscle
less elastic tissue
higher compliance
Veins are highly distensible, so they are called — — that act as
capacitance vessels blood reservoirs (60% of TBV)
Venous Pressure (2)
Pressure gradient available for venous return ~15 mm Hg. This is not sufficient to move blood back to the heart
Mechanisms supporting Venous Return
echanisms supporting Venous Return (4)
- Venous Valves
- Respiratory pump (thoracic pump): Pressure changes in the
central cavity due to the pressure changes due to breathing. This
helps to propel blood back to the heart. - Skeletal muscle pump: When muscles contract they squeeze the
veins. This results in blood moving toward heart. Venous valves
prevent backflow when the muscle relaxes. - Venoconstriction: The smooth muscle in the veins is under SNS
control (α adrenergic receptor) and contracts when stimulated.
Varicose Veins
Veins have one-way valves that prevent the
backflow of blood.
Varicose veins are
veins that have become
dilated and tortuous resulting in incompetent
(leaky) valves.
who suffers from varicose veins?
15% of adults suffer from this condition,
mainly in the lower limbs.
Capillaries
Anatomy (2)
Single layer endothelial cells
Basement Membrane
Mechanisms of Capillary Exchange (6)
Narrow water filled spaces
Movement of fluid and dissolved substances via Bulk Flow (decrease ΔP)
Vesicle fuse to form water filled channel
Movement of fluid and dissolved substances via Bulk Flow (decrease ΔP)
Transcytosis and Transepithelial Transport
Simple Diffusion
What is the difference between Plasma and Interstitial Fluid?
plasma has more proteins
Metarteriole/Thoroughfare Channel (2)
Intermittent Smooth Muscle
Most direct route between
arteriole and venule
Capillaries (1)
Branch off Arteriole and Metarteriole
Precapillary Sphincters (2)
Smooth Muscle
Control entrance to capillaries
Arteriovenous Anastomosis (2)
Direct connection between arteriole and Vein
No Exchange
Amount of blood and pathway blood travels through capillary bed
varies moment to moment based on
tissue’s metabolic activity
Capillary Network
Regulation (4)
Metarteriole and Precapillary sphincters fluctuate between contracted and relaxed state Rate of fluctuation controlled primarily by [O2 ] in tissue [O2] low, smooth muscle spends more time in relaxed state and blood takes convoluted path through capillary bed [O2] high, smooth muscle spends more time in contracted state and blood takes most direct path through capillary bed
Velocity is slowest in
capillary
beds because they have a
greater cross-sectional area
Diffusion Across the Capillary Wall: Exchange of (2)
Nutrients and Metabolic End Products
Bulk Flow (2)
Water distribution between plasma and interstitial fluid
Movement of protein free fluid between plasma and interstitial fluid
bulk flow occurs through
water filled channels
bulk flow function
Distribution of ECF volume (not exchange of
nutrients and metabolic products which occurs more rapidly
via diffusion).
Two Directions Fluid Movement (2)
- Filtration
2. Absorption
**Magnitude and Direction of fluid movement determined by
ΔP
- Hydrostatic Pressure of Capillary (PC)
Force exerted by the fluid pressing against a capillary wall (Capillary Blood Pressure) Filtration Force (30 mmHg arterial end; 10mmHg venous end)
- Colloid Osmotic Pressure in Capillary (ΠC) (2)
Osmotic force created by impermeable plasma proteins Absorptive Force (28 mmHg)
- Hydrostatic Pressure of Interstitial Fluid (PIF) (2)
Force exerted by the fluid in the interstitial space
Absorptive Force; (-3mmHg)
- Colloid Osmotic Pressure of Interstitial Fluid (ΠIF) (2)
Force exerted by the impermeable proteins in the interstitial space
Filtration Force; (8 mmHg)
Net Filtration Pressure =
PFiltration – PAbsorption
Pc + πif) – (πc + Pif
The Starling Equation also accounts for the
water permeability of the capillary (Kf)
Net Filtration Pressure = Kf [(Pc + πif) – (πc + Pif)]
+ value = net filtration
- Value = net absorption
Filtered fluid returned
to CV system by
lymphatic system
Overall Net Filtration Pressure (2)
Varies based on status of arterioles feeding capillary bed
Arteriolar dilation and constriction alter PC and overall net filtration pressure
Lymphatic System
Functions: (3)
- Return filtered fluid and proteins to circulation
- Transporting absorbed fat from small intestine to circulation
- Immune System (fluid percolates through lymph nodes as
returns to circulation)
- Return filtered fluid and proteins to circulation (5)
a. Normally produce ≈ 3L filtrate/day
b. Escaped Proteins
Normally small amount filtered
Injury
Hormones and Paracrines (ex. Histamine, Bradykinin)
Mechanism of Lymph Flow (3)
Smooth muscle in the wall of the lymphatics exerts a pumplike action.
Lymphatic vessels have valves similar to those in veins.
Skeletal muscle pump and Thoracic pump
Edema
Fluid accumulation in interstitial space
Edema causes loss of (2)
- Loss of normal lymph drainage
2. Loss of normal balance between PC and ΠC
- Loss of normal lymph drainage (2)
Blocked by parasites (ex. Bancroftian Filariasis (Elephantiasis))
Removal/Damage during surgery
- Loss of normal balance between PC and ΠC (3)
A. increase PC
B. decrease ΠC
C. increase Πif
Causes & Examples of Edema Formation (4)
Increased Pc
Decreased πc
Increased capillary permeability
Impaired lymphatic drainage
Cause: Increased Pc
Ex: (5)
Arteriolar Dilation Venous Constriction Increased Venous pressure Heart failure NOT increased MAP
Cause: Decreased πc
Ex: (4)
Decreased plasma protein concentration
Severe liver failure (lack of plasma protein)
Protein malnutrition
Nephrotic syndrome
Cause: Increased capillary permeability
Ex: (2)
Burn
Inflammation
Cause: Impaired lymphatic drainage
Ex: (3)
Standing
Removal of lymph nodes
Infection of lymph nodes
Edema Treatment (3)
- Ice
- Elevation
- Compression
