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Human Physiology
Digestive and Respirtory
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Digestive system
System responsible for breaking down food into
nutrients
that can be
absorbed
and used by the
body
Key components of the digestive system
Saliva
Esophagus
Stomach
Small
intestine
Large
intestine
Pancreas
Liver
Gallbladder
Saliva
Contains
amylase
which digests
starches
(carbohydrates)
Movement of food through the digestive system
1.
Food mixture
(bolus) moves down the
esophagus
via peristalsis
2. Food is churned with
acid
in the stomach and called
chyme
3.
Chyme
enters the
small intestine
4.
Digestion
is completed in the
small intestine
5.
Mixture
enters the
large intestine
Stomach
Acid kills
bacteria
and
starts digestion of proteins
and continues digestion of
starches
Small intestine
First section is the
duodenum
where
chyme
is neutralized
Digestion
is completed and digested products are absorbed from the
ileum
Large intestine
Water and vitamins are
reabsorbed
Anaerobic
bacteria can ferment undigested polysaccharides to produce
energy
Pancreas
Secretes
amylase
, trypsin and
lipase
into the small intestine
Liver
Secretes
bile
to
emulsify lipids
Gallbladder
Stores
bile
, which is not an enzyme and breaks down large
lipid
molecules
Layers of the small intestine
Serosa
Longitudinal muscles
Circular muscles
Submucosa
Mucosa
Villi
Increase the
surface area
of the small intestine for
absorption
Digestion in the small intestine
1. Food is broken down into
monomers
2.
Pancreas
and intestinal wall secrete
enzymes
into the lumen
3. Pancreatic enzymes have an optimal pH of
neutral
to
alkaline
4. Enzymes include amylase, endopeptidases,
lipases
, phospholipases, nucleases, maltase,
lactase
, exopeptidases, and dipeptidases
Intestinal villi
Increase
surface area for absorption
Goblet cells produce
mucus
Capillary network and
lacteal
carry away
absorbed
nutrients
Products directly absorbed by villi
Bases
and
phosphates
from nucleic acids
Fatty
acids and
glycerol
Amino
acids
Monomeric
carbohydrates
Methods of absorption
1. Substances move from
lumen
into
epithelial villi
2. Amino acids and monosaccharides move from
villi
into capillaries, monoglycerides move into
lacteals
3. Absorption methods: simple diffusion,
facilitated
diffusion, active transport,
pinocytosis
Starch digestion in the small intestine
1.
Amylase
breaks down starch into
maltose
, maltotriose and dextrins
2. Maltase,
glucosidase
and dextrinase break down these into
glucose
which is absorbed
Transport of absorbed nutrients
All absorbed monomers are transported via the
hepatic portal vein
to the
liver
, then enter the general circulation
Ventilation
Breathing
in and
out
Ventilation
Maintains oxygen and carbon dioxide concentration gradients
Replaces low oxygen air with high oxygen air
Gas exchange
Depends on
oxygen
and
carbon dioxide concentration gradients
Facilitated by
thin alveolar
walls and
moisture
Types of alveolar cells
Type
1
pneumocytes (thin for gas exchange)
Type
2
pneumocytes (secrete surfactant)
Ventilation mechanism
1. Thorax expands during
inspiration
,
decreasing
pressure and drawing air in
2. Thorax
contracts
during expiration, increasing pressure and forcing air
out
Muscles involved in
ventilation
External
and
internal
intercostal muscles are antagonistic
Diaphragm
contracts to increase
thoracic
volume
Lung cancer
Most common form of cancer, mainly caused by
smoking
, results in
shortness
of breath, cough, chest pain
Emphysema
Caused by long-term exposure to cigarette smoke, results in
inflammation
, narrowing of airways, and breakdown of
alveolar walls
Alveoli
Site of
gas exchange
Type 1
pneumocytes
provide
large
surface area
Type 2
pneumocytes
secrete
surfactant
Blood pH
regulation
Buffers
in blood plasma and tissue fluids maintain
pH close
to neutral
CO2 lowers
pH, forming
carbonic acid
and hydrogen ions
Adult hemoglobin
Composed of 2 alpha and 2 beta chains, each with a
heme
group containing
iron
Fetal hemoglobin
Has
2
alpha and 2 gamma peptides, allowing
higher
oxygen affinity than adult hemoglobin
Myoglobin
Protein used to bind
oxygen
in muscles, has higher affinity for oxygen than
hemoglobin
Oxygen transport in blood
Oxygen
binds to hemoglobin in the lungs, causing an allosteric change that increases
oxygen
binding affinity
Carbon dioxide transport in blood
CO2 dissolves in plasma, binds to
hemoglobin
as
carbaminohemoglobin
, or is converted to carbonic acid and bicarbonate ions
Bohr shift
Increased oxygen concentration decreases hemoglobin's affinity for oxygen
Gas exchange during exercise
Increased tissue demand for
oxygen
is met by
increased
rate and depth of breathing, controlled by the respiratory control centre
Gas exchange at high altitude
Lower
oxygen
concentration leads to
decreased
hemoglobin affinity for oxygen, reducing oxygen supply to tissues