BLOOD SUGAR REGULATIONhomeostasis

• Need to maintain 4-6 millimoles/L of sugar in blood• Organs involved: • Pancreas / adrenal glands (hormones)• Liver

1. Liver• Liver is connected via hepatic portal vein to:• Stomach• Spleen• Pancreas• Intestines

Liver (cont.)• Liver has 4 functions for glucose:• Removed by liver for energy in Liver• Removed by liver or muscles & converted to glycogen (for

storage)• Circulated in blood to be available for body cells to use (as

energy)• Excess is converted into fat (long-term storage)

• Body stores approx 500g glycogen (100g in liver, remainder in muscles)

• Glycogenesis: glucose glycogen (influenced by insulin – from pancreas)

• Glycogenolysis: glycogen glucose (influenced by glucagon – from pancreas)

• Glycogen in Liver: enough reserves for 6hrs, after that need to start converting fat

2. Pancreas• Islets of Langerhans:• Alpha cells: glucagon• Beta Cells: insulin

Insulin: (decrease blood sugar) from Beta cells• Accelerates transport of glucose from blood to cells• Accelerates ‘glycogenesis’ (glucose glycogen)• Stimulates glucose fat (adipose tissue)• Increases protein synthesis in some cells

Glucagon: (increase blood sugar) from Alpha Cells• Stimulates ‘glycogenolysis’ (glycogen glucose)• Stimulates ‘gluconeogensis’ (fat/amino acid sugar

molecules)• Stimulates protein breakdown

3. Adrenal Glands3 hormones:• Cortex: • glucocorticoids (eg cortisol)

• Medulla:• adrenaline• Noradrenaline

Glucocorticoids (increase blood sugar)• Stimulated from anterior pituitary (ACTH)• Stimulate glycogenolysis (glycogen glucose)• Increases rate by which amino acids are removed by cells &

transported to liver for gluconeogenesis (fat/amino acids glucose)

• Promotes mobilisation of fatty acids from adipose to allow fat glucose

Adrenal Glands (cont.) • Adrenalin / Noradrenaline: (increase blood sugar)• Stimulates glycogen (in muscle cells) lactic acid glucose

(in liver)• Stimulates glycogenolysis

*Note: • glucagon’s target organ is the liver• Adrenaline/noradrenaline’s target organ is the liver and

the muscles.

Gas concentrationshomeostasis

Control of Breathing• Diaphragm & intercostals require stimulation from nerves to

contract. (unlike heart)• Phrenic nerve (a spinal/cervical nerve from neck thorax)

diaphragm• Intercostal nerve (a spinal/thoracic nerve from neck thorax)

Intercostal muscles• Controlled by respiratory centre in lower medulla• 2 regions: expiration & inspiration• Chemoreceptor’s (conc. of chemicals in plasma- specifically

CO2, O2 , and H+):o Aortic – in aortao Carotid bodies – in carotid (neck) arteryo Medulla Oblongata

Conc .of O2: • Receptors in Medulla, Carotid, and aortic bodies. • only a large change will have an effect

Conc. of CO2: • small change results in a large response but

chemoreceptors are only located in medulla (70-80% of breathing rate changes are a consequence of CO2 change detection)

• Takes several minutes for response

Conc. of H+: • CO2 + H2O H2CO3 H+ + HCO3

-

• As H+ increase, pH decreases, Aortic & Carotid bodies are stimulated

• Faster response but not as sensitive as CO2

Stretch Receptors:• Stimulated when lungs inflate• Send impulses to inspiratory neurons in Resp. Centre of

Medulla & inspiration ceases, expiration begins• Not very sensitive, only a protective mech. to prevent

overstretching

Voluntary Control of Breathing• Connectors from Cerebral Cortex to descending tracts in

spinal cord• Protective device stops us inhaling water, irritating gases

etc.• Hyperventilation: Rapid deep breathing, Increases O2,

decreased CO2

• Dangerous as if done before swimming as: Can hold breath longer but not because of abundance of O2, but lack of CO2

Exercise and Breathing rate:• Depth & rate must increase• Heavy exercise can cause 10 – 20x more ventilation• Due to fluctuations in O2, CO2 & H+ conc.

Blood Pressure/ heart ratehomeostasis

Cardiac Output• Heart rate: number of times heart beats/min

• Stroke volume: vol of blood forced from a ventricle/contraction

• Cardiac Output: vol of blood leaving ventricle / min• Cardiac Output = Stroke vol x Heart rate

• Venus return: return of blood to heart

• Blood Pressure: Pressure of blood on vessel walls• Influenced by: cardiac output & diameter of blood vessels

Regulation of heart rate- Specialised cells which initiate impulse in heart:

o Sinoatria node (SA node) – in right atrium Causes both atria to contract Can be influenced by sympathetic (noradrenaline) and

parasympathetic NS (acetylcholine)

o Atrioventricular node (AV node) -in septum between two atria (near AV valves) After being stimulated by Av node, conducting fibres

from Av node pass impulse to both ventricles May be stimulated by sympathetic NS (noradrenaline)

Regulation of heart rate (cont.)- Heart can be influenced by brain/CNS (Cardiovascular

Regulating Centre) in Medulla Oblongata to SA node or AV node

- Detected by pressoreceptors: (baroreceptors) detect blood pressure

Factors influencing stroke Volume

- Length of diastole: period of relaxation between contractions. (time to fill up)

- Venus return: contraction of the muscle fibres of the heart is more forceful when fibres are stretched (elasticity) influenced by activity of skeletal muscles, respiratory movements, tone of vein walls, reduced friction in vessels

- Autonomic nervous system

Other factors:- Age: Highest at birth, slows down towards old age Ave (70-

80 bmp)- Sex: females faster- Emotional state: strong emotions (anger, fear, anxiety)

increase & depression, grief decrease.

Blood Flow

- Amount of blood flowing through an organ or vessel (mL/min)

- Determined by:o Cardiac output o Diameter of arterioles. Determined by:

CNS Hormones (adrenaline – vasodilator in muscle,

vasoconstrictor everywhere else) CO2, lactic acid: Vasodilator, O2: Vasoconstrictor

e.g Exercise

- Output of heart may rise from 5L/min to 30L/min