Describe the origin of the heartbeat and the nervous control of the heart rate
- Is initiated by the sinoarterial (SA) node
- SA node pacemaker cells generate an electrical impulse (action potential)
- Spreads across atria causing contraction
- Pauses at AV node before spreading down conducting fibres to ventricles causing contraction
- HR modified by autonomic nerves and hormones
Describe the origin of the heartbeat and the nervous control of the heart rate
- SNS
• SNS – somatic nervous system
- Fight or flight
- EEE (excitement, exercise and emergency)
- Increase HR
Describe the origin of the heartbeat and the nervous control of the heart rate
- PNS
• PNS – parasympathetic nervous system
- Rest or digest
- DDD (digestion, defecation and diuresis)
- Decreased HR
- Diuresis = increased or excessive production of urine
Have an understanding of the normal heart rate of domestic animals and normal variations in heart rate
Species Age HR (beats/min) Cattle Adult 60-70 Calf 100-140 Sheep Adult 70-80 Lamb 120-160 Goat Adult 70-80 Kid 120-160 Horse Adult 28-44 Foal 60-80
Pig Adult 60-80
Dog Adult 70-120
Chicken Adult 200-400
Define tachycardia and bradycardia and list some common causes of each
• Tachycardia
- Abnormally elevated resting HR
- Causes can include: stress, heat, fever, drugs and many formal of heart and vascular disease
Define tachycardia and bradycardia and list some common causes of each
• Bradycardia
- Abnormally low resting HR
- Less common than tachycardia
- Causes can include: electrolyte imbalance, drugs and some heart disease
List the major components of blood and describe their major functions
• Transportation
• Transportation - Gases (O2 and CO2) - Nutrients and wastes - Hormones • Osmotic pressure - H2O • Onconic pressure - Proteins • Heat • Immune cells and antibodies • Haemostasis - Platelets and clotting factors • Buffers - Regulate pH
List the major components of blood and describe their major functions
• Plasma
• Plasma = 55 – 70% of total blood volume
- Water 92%
- Proteins 7%
- Other 1%
• Plasma proteins generate colloid osmotic (onconic) pressure, important in balancing fluid movement in & out of capillaries
List the major components of blood and describe their major functions
• pH
Maintains pH, specific functions (lipoproteins), immunity (immunoglobins/antibodies), coagulation (clotting)
List the major components of blood and describe their major functions
• Red Blood Cells
• Cells = 30 – 45% of blood volume - RBC - WBC - Platelets • RBC >90% of all blood cells, required for O2 transport, contains haemoglobin (readily binds to O2), biconcave disk for gas diffusion, mature cells have no nucleus
List the major components of blood and describe their major functions
• White Blood Cells
• WBC (leukocytes) body defence against pathogens (bacteria, parasites and viruses)
- Granulocytes – neutrophils, eosinophil’s and basophils
- Monocytes
- Lymphocytes
List the major components of blood and describe their major functions
• Platelets
• Platelets (thrombocytes)
- Small cytoplasmic fragments, prevents blood loss (haemostasis)
- Binds damaged cells, swells, stick together = platelet plug
- Platelet plug is reinforced by polymerized proteins (coagulation factors) to form final blood clot
Be able to calculate packed cell volume (PCV)
- RBC/total volume x 100% = PCV
* % Of RBC in blood
Describe what happens to packed cell volume and protein when hydration changes
• When dehydration occurs, normal plasma volume decreased, and protein concentration increased. RBC concentration is increased.
- Describe the five types of blood vessels, including how their function relates to their structure.
• Arteries and arterioles
- Takes blood away from the heart
• Arteries - large branching vessels, thick walled, muscular and highly elastic, pressure reservoirs, recoil of elastic walls during diastole ensures continuous blood flow, important to maintain pressure during diastole
• Arterioles – small branching vessels, carries blood away from heart to capillaries, very little elastic tissue but not a lot of smooth muscle, high resistance, muscle permits change in diameter to alter resistance and blood flow (vasoconstriction/dilation). Important to maintain arterial BP and flow through organs.
- Describe the five types of blood vessels, including how their function relates to their structure.
• Venules and veins
- Takes blood back to the heart
• Venules – capillaries come together to form venules, venules contain little or no smooth muscle, carry blood to veins (to heart), some exchange can occur here
• Veins – approx. same size as arteries but thinner walls, little or no elastic tissue, thin muscle layer, expand easily and act as a site for blood storage, 60% of blood volume is in the systemic veins, vasoconstriction pushes stored blood back to heart, pressure in veins low
• Blood flow maintained by - Low resistance
- One-way valves
- Skeletal muscle pumps
- Describe the five types of blood vessels, including how their function relates to their structure.
• Capillaries
- Connect arterial and venous sides
• Capillaries – smallest vessels in the body, primary site of gas, nutrient, and waste exchange, most cells are 1mm of a capillary, thin walled and porous, don’t exist on its own but in capillary beds or networks, extensive branching increases surface area
• Regulated by: - Pre-capillary sphincters: smooth muscle surrounding capillaries at atriole end
- Metarterioles: a shunt between arteriole and venule
• Not just passive pipes – they have difference structures and functional roles
Describe the two factors that determine blood flow
- Pressure Gradient
• Pressure gradient (ΔP) and resistance to flow (R)
• Pressure gradient
- Blood flows from high pressure in arteries to low pressure in the veins
- Blood is under pressure from contraction of the heart
• Resistance
- Pressure falls along a vascular circuit (resistance)
Describe the two factors that determine blood flow
- Resistance
• Pressure gradient (ΔP) and resistance to flow (R)
• Resistance
- Pressure falls along a vascular circuit (resistance)
List the three features which influence resistance to flow in a vessel
- Radius of vessel
- Length of vessel
- Viscosity of fluid
- As radius increases, resistance decreases = flow rate increases
Describe the role of vasodilation and vasoconstriction in regulating blood flow, and list the factors that influence these processes
- Vasoconstriction
• Vasoconstriction leads to increased TPR (total peripheral resistance) and decreased flow
- Increased SNS input
- Increased adrenaline in blood
- Local factors reduced metabolism in tissues (low CO2)
- Medications
• Vasodilation leads to decreased TPR and increased flow
- Decreased SNS input
- Decreased adrenalin in blood
- Local factors as increased metabolic activity (increased CO2)
- Medications
Describe the role of vasodilation and vasoconstriction in regulating blood flow, and list the factors that influence these processes
- Vasodilation
• Vasodilation leads to decreased TPR and increased flow
- Decreased SNS input
- Decreased adrenalin in blood
- Local factors as increased metabolic activity (increased CO2)
- Medications
Define the cardiac output, stroke volume and heart rate and give the relationship between these variables
- Cardiac output (CO): the amount of blood pumped out of the heart each minute (CO = SV x HR)
- Stroke volume (SV): the amount of blood pumped out of the ventricle each ‘stroke’ (L/beat)
- Heart rate (HR): represents the number of beats per minute
- Increased cardiac output = increased stroke volume or HR (or both)
List the factors that affect heart rate and stroke volume
• Heart Rate
- HR increased by SNS and circulating adrenalin
- HR decreased by PNS
- Changes in HR are seen in age, activity, fitness, fear, anxiety, excitement, response to blood volume drop/pressure, disease status
