what is homeostasis?
- Maintenance of nearly constant conditions in the internal environment despite changes in the external environment.
- Order depends on constant energy input from the external environment to reduce entropy (disorder/chaos) and maintain order for the internal environment, that is, the body
regulation of arterial blood pressure (ABP)
- several systems; one involves the baroreceptor system
- baroreceptors are cells that sense pressure and are
found in the aortic arch and carotid arteries - stimulated by stretch of arterial wall if ABP is high
- the impulses inhibit the vasomotor center in CNS
- this acts to diminishes heart activity and drives dilation
of peripheral blood vessels - reduces ABP
negative feedback: maintain a status
- Most common regulation mechanism
- e.g. fluid in = fluid out
- e.g. control of CO2
levels - e.g. blood glucose levels
positive feedback: go from point A to point B
- e.g. parturition (birth)
- e.g. nerve action potentials
- e.g. blood clotting cascades
Regulation of blood glucose level
High blood glucose level (hyperglycemic)
- after eating pancreas secretes insulin into blood
- liver stores glucose from blood as glycogen, muscle cells store glycogen and build protein, adipose tissue uses glucose from blood to form fat
- glucose level drops
Low blood glucose level (hypoglycemic)
- between eating pancreas secretes glucagon to blood
- adipose tissue breaks down at, liver breaks down glycogen to glucose, glucose enters blood
- glucose level rises
Homeostasis: blood calcium level
High blood calcium level
- stimulus: rising blood Ca2+ level
- thyroid gland releases calcitonin
- stimulates Ca2+ deposition in bones, reduces Ca2+ uptake in kidneys to be excreted as waste
Low blood calcium level
- stimulus: falling blood Ca2+ level
- parathyroid glands release parathyroid hormone (PTH)
- increases Ca2+ uptake in intestines, increases Ca2+ uptake in kidneys, stimulates Ca2+ release from bones
Regulation of core body temperature
High temperature
- sensors
- control center (hypothalamus)
- dilation of blood vessels in skin promotes heat loss, sweating
Low temperature
- sensors
- control center (hypothalamus)
- constriction of blood vessels in skin (saves heat), shivering (generates heat)
Blood is a ________ ______________ tissue
liquid connective
~60% of adult body is fluid (~42 liters)
– “60-40-20 rule”
– total body water = 60% of body weight
* intracellular fluid = 40% of body weight (28L)
* extracellular fluid = 20% of body weight (14L)
Extracellular fluid (20%) consists of:
– Plasma (~20% of total extracellular fluid)
– interstitial fluid (~80% of total extracellular fluid)
– transcellular fluid
* e.g., cerebrospinal fluid, ocular fluid, joint fluid, and bladder urine
* normally ignored in most calculations, though it may be as high as 1 L
* and note, they are all derived from blood
Blood contains
– contains both ICF (RBC) and ECF (plasma)
– blood considered distinct compartment
– average blood volume ~5 L and is ~7% body
weight
** approx. 55-60% (3 L) plasma; 45-40% (2 L) RBC **
* can vary according to gender; weight; age; health
Movement of extracellular fluid
through tissue
-Arteriole (oxygenated) -> capillary bed -> venule (deoxygenated)
- Most cells are located within 50 micrometers from a capillary, so they
readily exchange with blood supply. Without it, they usually will die
Acquisition and distribution of
nutrients
- Oxygen
– respiratory & cardiovascular system - blood picks up O2 from alveoli; diffusion
- cardiovascular system delivers
O2-laden blood to the cells
Removal of metabolic end products
(wastes)
- Carbon dioxide
– respiratory & cardiovascular
system - all cells produce CO2
- diffusion to ECF → plasma
- exit via the lungs
Blood after being spun in centrifuge (components of fluid)
- Cell volume = hematocrit
- Plasma (55%) = ECF
- Platelets and
WBC (1%) = ICF
-RBC (44%) = ICF
What is in blood?
Cellular components/Formed elements (45%)
- Platelets
- RBCs (erythrocytes)
- Leukocytes (WBCs): granulocytes = neutrophils, eosinophils, basophils; lymphocytes; monocytes
Plasma (55%)
- H2O (95%)
- Proteins: albumins, globulins, fibrinogen
- Solutes: electrolytes (Na+, Cl-, HCO3-), gases (O2, CO2), metabolic substances
In this tiny drop (1 mm3) there are millions of _____, hundreds of thousands of ___________, and thousands of ______.
RBC
platelets
WBC
Circulatory system
- Heart is main pump
- Big vessels → small → big
– Arteries away from heart (ventricle ejection)
– Arterioles
– Capillaries
– Venules
– Veins back to heart (dump into atria)
Not all veins carry deoxygenated blood, not all arteries carry deoxygenated blood
Pulmonary veins: These veins are the exception to the rule that veins carry deoxygenated blood. They carry oxygen-rich blood from the lungs to the heart.
Pulmonary arteries: These arteries are the exception to the rule that arteries carry oxygenated blood. They carry deoxygenated blood from the heart to the lungs.
Arteries/arterioles
– Withstand high pressure
– Their walls have 3 layers:
* Thin inner epithelium (intima)
* Thick smooth muscle layer (media)
* Outer connective tissue (adventitia)
Veins/venules
– Their walls have 3 layers
* Thin inner epithelium
* Thin smooth muscle layer
* Outer connective tissue – not as thick as arteries/arterioles
* One way valves to help return one way back to heart
* Lower pressure, larger volume than artery system
Capillaries are microscopic vessels between
arterioles and venules
– Generally made of one cell layer of endothelial tissue
– Form beds of vessels where fluid exchange with body cells occurs
– Create large surface area
Pulmonary circuit
the right side of the heart that receives
blood from the body and sends it to the lungs
Systemic circuit
the left side of the heart that receives blood
from lung and sends blood to the entire body
