Organ Integration and Control
Summary
Table 22-2
Metabolism Review
1. Glycolysis – breakdown of glucose to pyruvate
2. Gluconeogenesis – synthesis of glucose
3. Glycogenolysis – breakdown of glycogen
4. Glycogenesis – synthesis of glycogen
5. Lipolysis – breakdown of lipids
6. Lipogenesis – synthesis of lipids
Metabolism Review
1. Tricarboxylic Cycle – Oxidation of Acetyl CoA
2. beta Oxidation – breakdown of fatty acids to Acetyl CoA
3. Pentose Phosphate Pathway – synthesis of pentose sugars
and reducing power
4. Urea Cycle – breakdown of amino acids
Energy
Metabolism
Gluconeogensis
Anaerobic Respiration
Aerobic Respiration
Figure 4-13
Erythrocyte Metabolism
Erythrocytes are very simple creatures:
1.
2.
They have no nucleus
They have no mitochondria
The main metabolic pathways include Glycolysis and Pentose Phosphate Pathway.
No lipid or amino acid metabolism, no Kreb’s cycle.
Erythrocytes consume glucose and dump lactate
and pyruvate into the blood stream.
Most of the ATP generated is used to power the Na-K ATPase pump which in
turn helps maintain the shape of the cell. The biconcave shape maximizes the
area/volume ratio (a sphere has a larger area to the given volume).
Liver Metabolism
The liver is metabolically a complex organ. For the purposes of this class the
following relevant property is important:
The liver operates as a buffer organ against fluctuations in the nutrition state
in order to maintain relatively constant levels of metabolites in the blood stream.
The liver will:
1.
2.
3.
4.
5.
6.
7.
… absorb nutrients coming from the small intestine.
… take up glucose and store it as glycogen or convert it to fatty acids.
… release glucose into the blood stream by breaking down Glycogen.
… take up lactate and some amino acids (ala) and convert it into glucose.
It also has the capacity to form ketone bodies from fatty acids.
… degrades excess amino acids into Urea for excretion
Stores some vitamins and minerals.
8.
Other functions include detoxification and the formation of bile
Liver Metabolism
Urea
Glucose
Ketones
Lactate
Fatty Acids
Amino Acids
Glucose
From Small Intestine
Liver Metabolism: Absorptive State
Liver Metabolism: Absorptive State
1.
2.
3.
4.
5.
Excess glucose is stored as glycogen
Muscle stores glycogen
Muscle synthesizes new protein from amino acids
Adipose tissue stores fatty acids (from liver) as fats
Glucose is the preferred energy source for organs such
as heart and brain
Liver Metabolism: Postabsorptive State
Liver Metabolism: Postabsorptive State
Glycogen is broken down and released as glucose
(The Brain and Red blood cells rely heavily on glucose)
The liver stores about 12 to 24 hours of glycogen reserves.
The blood stream itself stores only a few minutes worth of glucose.
Liver Metabolism: Postabsorptive State
Once glycogen reserves are exhausted gluconeogenesis begins.
In this mode glucose can be made from a number of sources
including:
1. Glycerol from fat breakdown
2. Alanine from protein breakdown – alanine cycle
3. Lactate (Red blood cells, Muscle) – Cori Cycle
Sources of Glucose
Figure 22-7
Prolonged Fasting (Starvation)
Once glycogen reserves are used up, the body starts to
breakdown fat to extract the glycerol and fatty acids.
The glycerol is used to make glucose but the fatty acids are used
directly by many organs as a source of energy (not brain or RBC).
As fatty acid metabolism increases the liver begins to convert
some of the acetyl-CoA in so-called ketone bodies.
Acetoacetate, 3-hydroxybutyrate, Acetone.
Acetone can’t be metabolized and is released in urine and
the lungs (hence the sweet small in the breath (ketosis) when
starving)
Ketone Bodies
Prolonged Fasting (Starvation)
Once the fats reserves are used up the only readily available
resource left is the protein found in muscle. Muscle protein
is degraded and concerted to amino acids, which the liver
converts to glucose. Finally once muscle protein is exhausted all
that is left is essential protein, which is then broken down.
For a healthy individual, starvation can last 40 to 50 days before
death ensures, this assume that water is not withheld.
Hormones
There are about 100 hormone and hormones like substances in the human body.
Chemically most hormones are either amino acid derivative, peptides or steroids.
Hormones carry out many functions, including:
1.
2.
3.
4.
Growth, differentiation of cells tissues and organs.
Control of metabolic pathways
Control of digestive processes
Maintenance of ion concentrations (water balance)
The hormone like substances include neurotransmitters and cytokines (immunity)
Figure 22-2
Hormone Action: Endocrine
Paracrine and Autocrine Modes
Table 22-3
Figure 22-14
Table 22-4
Figure 22-15