Homeostasis of blood sugar and gas concentration Flashcards
What is the use of glucose?
Glucose is the source of energy for cells’ activities.
Energy is released from glucose molecules by cellular respiration.
When is carbohydrates broken down into glucose?
digestion
Where is glucose absorbed into the. blood?
Through walls of small intestine
BGL after meal
After a meal, blood glucose concentration can rise sharply.
Homeostatic mechanisms then begin to operate to reduce the blood glucose concentration and maintain it at the normal level
Any excess glucose in the blood must be removed and stored ready for use in cellular activities between meals.
Main organs involved in blood sugar regulation :
Pancreas
Liver
Adrenal glands
what is Glycogenesis?
Formation of glycogen from other carbohydrates, esp
glucose
What is Glycogenolysis?
Breakdown of glycogen into glucose
What is Gluconeogenesis?
Conversion of fats or proteins into glucose
What is Lipogenesis?
Conversion of glucose to fat or the synthesis of fatty acids from glucose
What is the role of liver in BGL
Converts:
glucose into glycogen for storage
glycogen to glucose for release into the blood.
Most of the liver’s blood supply comes through the:
Hepatic portal vein
brings blood directly from the stomach, spleen, pancreas and small and large intestines.
Thus, the liver has the first chance to absorb the nutrients from digested food.
What happens to glucose in the liver?:
- Used by liver cells as an energy source.
- Converted into glycogen for storage (glycogenesis).
- Continue to circulate in the blood, available for body cells to absorb and use as a source of energy.
- Converted into fat for long-term storage (lipogenesis)
Explain glycogenesis
Glucose molecules are chemically combined to form glycogen.
Stimulated by the pancreatic hormone insulin.
Glycogen are stored in the liver and muscle cells.
Explain glycogenolysis
Occurs when the level of glucose in the blood drops below normal
Glycogen stored in the liver and muscle cells can be broken down into glucose.
Stimulated by another pancreatic hormone, glucagon
What is the role of pancrease
The cells in the islets of Langerhans are of two types:
Alpha cells secrete glucagon
Beta cells secrete insulin
What is the role of insulin?
Decreases in blood sugar levels in two main ways:
promotes transport of glucose from the blood into the cells
stimulates the conversion of glucose into glycogen
Also stimulates the conversion of glucose into fat in adipose tissue & increase in protein synthesis in some cells.
What is the role of glucagon?
Causes an increase in blood sugar levels.
Stimulates:
Glycogenolysis – the conversion of glycogen into glucose in the liver.
Gluconeogenesis - the conversion of fats and amino acids into glucose in the liver.
What is the role of adrenal glands?
Each gland is composed of two distinct parts:
outer part is called the cortex
inner part is the medulla
What stimulates adrenal cortex and what it releases?
Stimulated by adrenocorticotropic hormone (ACTH) from anterior pituitary. Secrete glucocorticoids (including cortisol):
The effect of cortisol released by adrenal cortex:
Stimulate the conversion of glycogen into glucose
Stimulate amino acids removal from cells (mainly muscle cells) & conversion of amino acids into glucose in the liver
Promote the mobilization of fatty acids from adipose tissue. Lipolysis of storedlipidsin the adipose tissue to release free fatty acids
muscle cells shift from glucose to fatty acids for much of their metabolic energy.
What does the adrenal medulla synthesis?
Synthesizes adrenaline and noradrenaline
How does adrenaline and noradrenaline effect the blood glucose level ?
Stimulates breakdown of glycogen into glucose in the liver
Stimulates the production of lactic acid from glycogen in muscle cells. Lactic acid can then be used by the liver to manufacture glucose.
What is the function of circulatory system ?
carries oxygen from the lungs the cells where it is used
takes away the carbon dioxide produced by cells the lungs for excretion
Groups of cells that are sensitive to changes in the concentration of oxygen, carbon dioxide, & H+ in the blood plasma:
Central chemoreceptors in the medulla oblongata
Peripheral chemoreceptors:
Aortic bodies
Carotid bodies
What is the modulator of the circulatory system ?
the respiratory centre located in the medulla oblongata
What is the effector of the circulatory system ?
Effectors:
Diaphragm
muscles that cause air to move in and out of the lungs
separates the thorax from the abdomen
Intercostal muscles
muscles between the ribs
What are stimulation in the respiratory system ?
Require stimulation from nerve impulses to initiate contraction
Diaphragm is stimulated by impulses from the phrenic nerve
Intercostal muscles are stimulated by impulses from the intercostal nerves
What type of nerves of the phrenic and intercostal nerves?
These spinal nerves have their origin in the spinal cord at the level of the neck and thorax
If these nerves are injured = complete paralysis of the muscles that ventilate the lungs
Death inevitably follows unless some form of artificial respiration is rapidly applied
How does the oxygen concentration affects the respiratory system?
If the concentration of oxygen falls below normal while other factors are held constant, the breathing depth & rate increases.
However, within the normal range of blood oxygen concentration, the effect on breathing rate is only slight.
The concentration has to fall to very low levels before it has a major stimulatory effect.
How does the carbon dioxide concentration affects the respiratory system?
Major factor in the regulation of breathing rate
Small increase in the concentration of CO2 is enough to cause a marked increase in the depth & rate of breathing
How does the hydrogen concentration affects the respiratory system?
Concentration of CO2 in the blood plasma affects the concentration of H+ ions.
H+ concentration of the blood increases, the pH decreases, causing an increase in the breathing depth & rate
Explain the voluntary control of breathing ?
Humans are able to voluntarily control their rate and depth of breathing & can stop breathing for a limited period
Voluntary control : connections from the cerebral cortex to descending tracts in the spinal cord.
Bypasses the respiratory centre in the medulla oblongata
Protective device: enables us to prevent irritating gases and water from entering the lungs
Build-up of CO2 in the plasma > eventually forced to take a breath
Explain hyperventilation
Rapid, deep breathing can provide more O2 than required and remove more CO2 than necessary
Can occur voluntarily or stimulated by physical stress or emotional stress
Usually corrects itself because of reduction in CO2 concentration
Why is hyperventilating dangerous?
Hyperventilating before swimming under water - dangerous!
Does allow a person to stay under water longer, but this is not because of extra O2 in the blood – it is due to the loss of CO2
Individual loses consciousness from lack of O2 to the brain before feeling the urge to breathe
What does exercise affects the breathing rate and depth ?
Increases both the rate of breathing and the depth of breathing
Contracting muscle cells require large amounts of O2 and produce large amounts of CO2
Increased demand for gas exchange
What is Heart rate?
number of times the heart beats per minute
What is Stroke volume ?
volume of blood forced from the heart with each contraction
What is Blood pressure ?
the force with which the blood presses on the walls of the blood vessels.
What is cardiac output?
– as cardiac output increases, blood pressure increases
- cardiac output - heart rate x stroke volume
What is diameter of blood vessels ?
constriction of blood vessels increases pressure and dilation decreases blood pressure.
What is the function of sinoatrial node ?
Sinoatrial node (SAN)
described as the ‘pacemaker’
responsible for the rhythmical contractions of the heart
Can stimulate heartbeat on its own but its activity is influenced by the autonomic nervous system
Describe the process of heart beats
When the heart beats, the following occur:
The SAN sends out nerve impulses that spread through the atria.
The stimulus reaches the Atrioventricular Node (AVN). At about this time, contraction of the muscle of the atrium begins.
Stimulation of the AVN causes it to send out its own impulses. These travel down the fibres in the septum between the ventricles.
The impulses then spread through the muscles of the ventricles. Atrial contraction is now complete and ventricular contraction begins.
Changes to blood flow during exercise
Large increase in blood flow is required by contracting muscles
to ensure an adequate supply of O2 and nutrients
to remove CO2 and heat produced
To ensure that blood supply to the muscles is increased:
blood vessels in internal organs such as the alimentary canal constrict.
dilation of blood vessels in the muscles.
The effect behavior of exercising
When a person is about to begin exercising, there is an anticipatory response brought about by the autonomic nervous system & by release of the hormone adrenaline
Blood glucose rises due to mental stress
Heart rate and stroke volume increase
When we exercise:
breathing rate and depth will increase
cardiac output will rise further
blood glucose will continue to be at a high level
Increase in blood supply to skeletal muscles
