Premaster Geneeskunde 2023 –
Guyton and Hall Textbook of
Medical Physiology
Inhoud
Chapter 1: Functional Organization of the Human Body and Control of the “Internal Environment”....2
Chapter 2: The cell and its functions......................................................................................................6
Chapter 4: transport of substances through cell membranes..............................................................16
Chapter 5: membrane potentials and action potentials.......................................................................23
Chapter 6: Contraction of skeletal muscle............................................................................................30
Chapter 7: excitation of skeletal muscle: neuromuscular transmission and excitation-contraction
coupling................................................................................................................................................38
Chapter 8: excitation and contraction of smooth muscle ....................................................................42
Chapter 9: cardiac muscle; the heart as a pump and function of the heart valves...............................47
Chapter 16: The Microcirculation and Lymphatic System: Capillary Fluid Exchange, Interstitial Fluid,
and Lymph Flow...................................................................................................................................56
Chapter 34: Resistance of the Body to Infection: I. Leukocytes, Granulocytes, the Monocyte-
Macrophage System, and Inflammation...............................................................................................65
Chapter 35: Resistance of the Body to Infection: II. Immunity and Allergy..........................................72
Chapter 36: Blood Types; Transfusion; and Tissue and Organ Transplantation....................................80
,Chapter 1: Functional Organization of the Human Body
and Control of the “Internal Environment”
Physiology is the science that seeks to explain the physical and chemical mechanisms that are
responsible for the origin, development, and progression of life. There are various fields with their
own characteristics. For example: viral physiology, mammalian physiology or human physiology.
Human physiology attempts to explain the specific characteristics and mechanisms of the human
body that make it a living being. Pathophysiology is the study of disordered body function (look for
altered physiological processes during disease) and the basis of clinical medicine.
The cell is a basic living unit of the body, each is adapted to perform particular function(s). As long as
there are proper concentrations of oxygen, glucose, ions, amino acids and fatty substances in the
extracellular fluid (explained beneath), they keep maintaining their function.
Amounts of cells in the human body:
- Total body 35-40 trillion human cells (=35-40 biljoen cellen).
- Red blood cells (RBC) 25 trillion cells per person (=25 biljoen cellen).
For cells to function, they need energy. This is obtained when oxygen reacts with carbohydrate, fat
and proteins. When cells are destroyed, the remaining cells usually generate new cells until the
supply is replenished.
The gastrointestinal tract (GI-tract) contains 4000-1000 different species of microorganisms (MO) and
therefore outnumber the human cells there. MO are essential to provide vital functions for the host,
like digestion, nutrition and immunity. However, when communities of MO (=microbiota) inhibit the
body, they can also cause disease.
50-70% of the human body is fluid: a water solution with ions and other substances.
- 1/3th is called extracellular fluid: fluid in spaces outside cells. There is a constant motion
throughout the body and it moves through capillary walls to get mixture of blood and tissue
fluids. Extracellular fluid contains ions and nutrients to keep cells alive.
Other names for the extracellular are: internal environment and milieu intérieur (Claude
Bernard).
There are large amounts of Na+ (sodium), Cl- (chloride), HCO3- (bicarbonate), CO2 (carbon
dioxide: towards the lungs), waste products (towards the kidneys) and nutrients for cells
like oxygen, glucose, fatty acids and amino acids.
- Mostly intracellular fluid: inside cells.
Large amounts of K+ (potassium), Mg+ (magnesium), PO43- (phosphate).
Homeostasis: the maintenance of nearly constant conditions in the internal environment (Walter
Cannon). Ions, nutrients, waste products and constituents of the body are kept within ranges:
H (hydrogen) less than 5nm/L range.
Disease is considered to be a state of disrupted homeostasis. Homeostatic compensations may
represent trade-offs to maintain vital body function but may in the end contribute to additional
abnormalities of the body function.
Extracellular blood is transported in two stages: movement of blood through blood vessels and
movement of fluid between the blood capillaries and intracellular spaces between tissue cells.
,In resting state, blood passes the circulation once a minute. In active
state, this may become up to six times.
In capillaries, there is exchange of extracellular fluid (blood) and
interstitial fluid (intercellular spaces). Most molecules except for
plasma proteins (too big) can diffuse through the capillary walls. This
diffusion is caused by kinetic motion of the molecules in the plasma
and the interstitial fluid.
Cells mostly lay within 50μm from capillaries, so that diffusion can
happen within a few seconds.
There is continuous mixing of extracellular fluid (both plasma and
interstitial fluid), thereby maintaining homogeneity.
Uptake of bodily substances:
- In the respiratory system (the lungs), oxygen is taken up in
blood over the alveolar membrane from the alveoli. This
alveolar membrane is 0.4-2.0μm thick.
- In the GI tract, dissolved nutrients like carbohydrates, fatty
acids and amino acids are absorbed from digested food.
- In the liver and other metabolic functioning organs (fat cells,
GI mucosa, kidneys and endocrine glands), the chemical composition of substances can be
changed into more usable forms. The liver can also eliminate waste products and toxic
substances that are ingested.
- The musculoskeletal system (muscles etc.) provides motility for the protection against
adverse surroundings.
Removal of metabolic end products:
- In the respiratory system, CO2 is transported to the alveoli and released into air.
- The kidneys remove most end products of cellular metabolism, such as urea, uric acid,
metabolic waste products and creatinine. In addition, excess of water and ions is also
regulated in the kidneys. While on the other hand, substances needed by the body, can be
reabsorbed like glucose, amino acids, water and ions.
- In the GI-tracts, undigested materials and waste products are eliminated in the faeces.
- The liver detoxifies and removes ingested drugs and chemicals into bile that are eventually
eliminated in the faeces.
THE REGULATION OF BODY FUNCTIONS
- Nervous system: controls many muscular and secretory activities of the body. The nervous system
is composed of three major parts:
1. The sensory input portion: sensory receptors detect the state of the body and its
surroundings. Receptors are located in the skin, eyes, ears etc.
2. The central nervous system (or integrative portion): it is composed of the brain and the
spinal cord. The brain stores information, generates thoughts, creates ambition from sensory
input and determines reactions that the body performs in response to sensations. Formed
signals are transported from here through the motor output portion.
3. The motor output portion: the desired action is carried out.
, There is also the autonomic system, this system operates in a subconscious level and controls many
functions of internal organs like the heart and GI tract.
- Hormone system: hormones are chemical substances that are secreted by endocrine glands, organs
and tissues to regulate cellular function. The thyroid hormone increases the rate of most chemical
reactions in all cells. Insulin controls glucose metabolism, adrenocortical hormones control K + and Na+
and protein metabolism. Parathyroid hormone controls bone Ca 2+ (calcium) and PO43-.
The hormone system controls many metabolic functions of the body.
The body is protected by various mechanisms:
- Immune system: white blood cells, tissue cells derived from white blood cells, thymus, lymph
nodes and lymph vessels. They protect the body from pathogens by distinguishing own
bodily cells from foreign cells and substances and destroying invaders by phagocytosis of by
producing sensitized lymphocytes or antibodies to destroy or neutralize invaders.
- Integumentary system: the skin and its appendages. They provide a boundary between the
body’s internal environment and the outside world. This is important for protection,
temperature regulation and excretion of wastes. The skin comprises 12-15% of the body
weight.
Reproduction is the last part of homeostasis.
Control systems can work within organs to regulate functions or control interrelationships between
organs. One of these control systems is the system to regulate O- and CO2 within the body. This
mechanism depends on the chemical characteristics of haemoglobin, which is present in red blood
cells. Haemoglobin has a strong chemical affinity for oxygen. This way, oxygen is taken up in the lungs
and when the concentration in tissue fluids is too low, oxygen can be released to re-establish an
adequate concentration. This is called the oxygen-buffering function of haemoglobin.
CO2 is the major end product of oxidative reactions in cells, accumulation may cease all energy-giving
reactions in cells. Fortunately, higher than normal CO 2-levels excites the respiratory centre, causing a
person to breathe more rapidly and deeply so that the excess CO 2 is removed till normal levels.
Another control system is the baroreceptor system. Baroreceptors are located in the walls of
bifurcation in the arch of the aorta and the thorax. They are activated with stretching of the arterial
wall. When activated, barrages of nerve impulses are send to the medulla of the brain. Secondarily,
the vasomotor centre is inhibited which decreases the number of impulses transmitted from the
vasomotor centre through the sympathetic nervous system
to the heart and blood vessels. The effect is a diminished
pumping activity of the heart and dilation of peripheral
blood vessels, allowing increased blood flow through the
vessels, both giving a decrease in arterial pressure.
Conversely, a decrease in arterial pressure relaxes the
stretch receptors, the vasomotor centre becomes more
active causing vasoconstriction and increased heart
pumping.
The table below gives the appearance of important constituents and physical characteristics of
extracellular fluid.
