Health and Disease Week 26 Flashcards
What is the equation for mean arterial pressure?
cardiac output x peripheral resistance
What does Poiseuille’s law describe?
the factors that determine the flow through a tube in terms of pressure, flow and resistance
What is the equation for flow (Q)?
Q = delta P / R
flow = pressure gradient / resistance
What is the extended equation for flow?
Q = delta P x (pi x r^4) / 8 x L x n
resistance has its own equation which contributes to this equation
Which factors impact flow through a tube?
- pressure gradient
- radius of the tube
- length of the tube
- viscosity of the liquid
How does the length of a blood vessel impact flow (Q)?
- the longer the tube, the decreased flow
- however blood vessel length remains constant, so does NOT control blood flow
How does viscosity of the blood affect flow (Q)?
- the higher the viscosity, the lower the flow
- viscosity is related to the haematocrit which MAY change during dehydration
- the viscosity will remain constant under normal conditions, so we can ignore this
How does the radius of the blood vessel impact flow (Q)?
- the larger the radius, the faster the flow to the power of 4
- so if you double the radius, you increase the flow by x16
- resistance is caused by friction of liquid against vessel wall
- the radius of the blood vessels can be regulated by smooth muscle
define total peripheral resistance
the sum of the resistance of all the blood vessels the liquid must go through
What is the total peripheral resistance primarily regulated by?
the arterioles
How do the arterioles regulate total peripheral resistance?
- the largest blood pressure drop occurs from the arteries to arterioles
- the arterioles have much more resistance due to their small diameter, so create a pressure difference
What is the average blood pressure?
120 mmHg systolic and 80 mmHg diastolic
How can you measure blood pressure using Korotkoff sounds?
- pump the cuff up
- pressure in the cuff will get to above the arterial systolic blood pressure
- slowly release the pressure
- when the pressure in the cuff is slightly below arterial blood pressure, you hear Korotkoff sounds
- eventually, the sounds disappear when the pressure in the cuff is below your diastolic blood pressure
define pulse
the vibration of the arteries caused by the ejection of the blood from the heart (left ventricle) into the systemic circulation
Where is the pulse commonly measured at?
the radial artery (wrist) and the carotid artery (neck)
define pulse pressure
the difference between the systolic and diastolic pressure (the fluctuations in blood pressure caused by the heart’s contractions)
define mean arterial pressure (MAP)
the AVERAGE pressure over the cycle
How do we work out the mean arterial pressure (MAP)?
since the diastole is about x2 as long as the systole, we work it out by taking the diastolic pressure and adding a 1/3 of the pulse pressure
diastolic pressure + 1/3 pulse pressure
What is the equation for pressure?
pressure (mmHg) = height x density x gravity
Why do you feel faint when standing?
- the mean arterial pressure at the heart will be lower than in the head due to an increase in height
- blood pressure drop to the head makes you feel faint
Why do giraffes have a higher blood pressure than humans?
they are taller so need a higher blood pressure to pump blood further to the head - however, the pressure DIFFERENCE is the same to determine flow
define hypertension
when the blood pressure in the body is high
How do most medications to treat hypertension work?
by dilating the arterioles to reduce the resistance and therefore blood pressure
What 4 main issues can hypertension?
- stroke
- heart attack
- heart failure
- chronic kidney failure
What causes a stroke?
when increased blood pressure leads to the rupture of blood vessels in the brain
How does hypertension cause a heart attack?
when increased blood pressure leads to the rupture of the coronary blood vessels in the heart and insufficient blood flow occurs
How does hypertension cause heart failure?
the heart continuously tries to push blood flow against narrow arteries and the muscles get thicker and stiffer, leading to heart failure
How does hypertension lead to chronic kidney failure?
the high blood pressure can damage glomeruli
What are baroreceptors?
pressure receptors
What do baroreceptors do?
they act as sensors in the homeostatic maintenance of mean arterial pressure (MAP)
Where are baroreceptors located?
the aortic arch and carotid sinuses
What is nerve firing by baroreceptors proportional to?
the size and magnitude in CHANGE in the mean arterial pressure
What is the main drawback of baroreceptors?
their response is lost in minutes - they act as only a short-term sensor of blood pressure
Where are the signals from the baroreceptors signalled to?
the medulla oblongata in the brainstem - baroreceptors act through the autonomic nervous system
What does the medulla oblongata do in response to the baroreceptors signalling?
activate the autonomic nervous system and release hormones
What do the sympathetic nerves do to control blood pressure?
- increase cardiac output through heart rate and stroke volume
- increase peripheral resistance through arterial vasoconstriction by acting on a1-adrenergic receptors
- they stimulate the SA node through b1-adrenergic receptors
How do the parasympathetic nerves control blood pressure?
- inhibit heart rate ONLY by acting on the SA and AV nodes
- act through m2 receptors
How do arterial baroreceptors regulate hypotension?
- drop in blood pressure
- firing by arterial baroreceptors
- increased plasma adrenaline (activates sympathetic NS through hormones)
- sympathetic discharge to arterioles, veins, heart
- this increases cardiac output and peripheral resistance by increasing stroke volume constricting veins and arterioles
- switches off the parasympathetic NS
How is the mean arterial pressure regulated long-term?
by the kidneys - they regulate the blood volume
How do the kidneys deal with long-term high blood pressure?
- the kidneys excrete water and sodium in urine
- this reduces the plasma volume
- this decrease in blood volume leads to a decrease in venous pressure and therefore venous return
- reduced end-diastolic volume
- decreased stroke volume
- decreased cardiac output
- reduced mean arterial pressure
How do the kidneys regulate long-term increased blood volume?
they try to excrete excess water to maintain blood pressure by the same mechanism
What 3 factors are peripheral resistance and local blood flow modulated by?
local, hormonal and neural factors
What are the 3 ways local blood flow and peripheral resistance are modulated by local factors?
- the myogenic response
- vasodilation induced by metabolites
- autocoids
How is peripheral resistance and local blood flow controlled by neurones?
- from medulla oblongata
- sympathetic nerves release noradrenaline which acts on b1 and a2 adrenergic receptors to cause vasocontriction or dilation
- depends on the receptors expressed on that tissue
How is peripheral resistance and local blood flow modulated by hormones?
- the adrenal glands can release noradrenaline as a hormone rather than neurotransmitter
- released around whole body rather than locally
- depends on the receptor on different tissues
What does the body need to do during exercise?
- increase oxygen uptake and CO2 removal by increasing cardiac output
- increase blood flow to muscles, heart and skin
- stabilise arterial blood pressure despite changes in cardiac output and peripheral resistance
How does the body boost cardiac output?
- the brain prepares for exercise through the medulla
- the brain resets the baroreceptors to prepare them for changes in blood pressure so they don’t overreact
- the cardiac output is increased by increasing heart rate and stroke volume by the sympathetic nerves
What must the body do during strenuous exercise?
divert blood to the brain, skeletal muscle, skin and heart
How does the body deal with strenuous exercise?
- vasodilation occurs in the arterioles to the skin and muscles
- vasoconstriction to the abdominal area
- there will be an overall decrease in peripheral resistance and the blood flowing to the skin and muscles overcompensate what is not going to the abdominal area
- cardiac output increases, but total peripheral resistance increases, so there is a small increase in MAP
- the reset of the baroreceptors means they won’t overrespond
define the Valsalva manoeuvre
forced expiration against a closed or narrowed airway
How can the Valsalva manoeuvre lead to a heart attack?
- exhalation against a closed airway means pressure builds up in the chest
- pressure on the vein coming back to the heart reduces venous pressure
- reduced end diastolic volume and stroke volume and cardiac output
- reduced MAP
- decreased firing of baroreceptors
- heart rate increases to try to increase the MAP again
- when you breathe out, the chest pressure reduces
- central venous pressure increases suddenly, so does stroke volume and cardiac output
- leads to a spike in MAP
- heart attack or stroke
What are the 5 main functions of the musculoskeletal system?
- support
- movement
- protection
- producing blood cells
- storing minerals
What are the 3 main components of the musculoskeletal system?
- bones
- muscles
- connective tissue
What are the 3 types of connective tissue?
cartilage, tendons, ligaments
What is the difference between tendons and ligaments?
tendons connect muscles to bones and ligaments connect bones to bones
What are the 2 types of bones?
compact bones and spongy bones
What are the features of compact bones?
- strong, dense bones
- on the outside of the skeleton
What are the features of the spongy bones?
- lighter, more flexible bones
- on inside of the skeleton
What are the 3 main types of cartilage?
- fibrocartilage
- elastic cartilage
- hyaline cartilage
What are the features of fibrocartilage?
- found in areas that need to withstand pressure
- very compressible
Where is an example of where fibrocartilage is found?
in between the vertebrae of the spine and the knees
What are the features of elastic cartilage? Where is it found?
- very stretchy
- for example, the external ear and epiglottis
What are the features of hyaline cartilage and where is it found?
- most common type
- at the ends of most bones where it gives support (joint surfaces)
- examples are nose, ribs, larynx
What are the features of bone?
- blood cells formed here
- store minerals
- contain up to 20% water
- contain collagen
- different cell types
What are the features of cartilage?
- 80% is water
- made up of mostly 2 components: matrix and water
- only made up of 2 cell types - chondroblasts and chondrocytes
- NO blood supply
- matrix made up of mostly type II collagen and proteoglycans etc
What are the 2 divisions of the skeleton?
- axial skeleton
- appendicular skeleton
What are examples of bones in the axial skeleton?
bones in the head, vertebral column, ribs
What are examples of bones in the appendicular skeleton?
bones in the limbs, pelvis etc
What are the 4 shape classifications of bone?
- long bones
- short bones
- flat bones
- irregular bones
What are features of long bones?
- longer than wide
- support the weight of the body and aid movement
found in the lower limbs and upper limbs
What are features of short bones?
- cube-like in shape
- about equal in length with thickness
- provide support and stability
examples are bones in the hands and feet
What are features of flat bones?
- thin and flat bones
- may have a slight curve
- attachment point for muscles and protecting the internal organs
examples are bones in the thoracic cage, pelvis, skull
What are features of irregular bones?
- do not fit into any other classification
- have more complex shapes
examples are bones found in the vertebrae, jaw, face
What are the 5 main components of bone structure?
- periosteum
- compact bone
- spongy bone
- bone marrow
- endosteum
What are features of the periosteum?
- fibrous membrane that covers outside of bones
- where the blood vessels and the nerves that supply the bones are found
- contain cells involved in bone growth and repair
What are the features of the bone marrow?
two types - red and yellow marrow
What are the features of the endosteum?
- a thin membrane that lines the medullary cavity inside
- important in bone remodelling and repair
What are the differences between compact and spongy bone?
compact:
- outside of the bone
- made up of structures called osteons
- osteons give the support
- the compact bone is where the muscle attaches
spongy:
- inside the bones
- porous due to structures called trabeculae
- these reduce the weight of the bones
-bone marrow is found here
What are the 4 main types of bone cells found in bone tissue?
- osteogenic cells
- osteoblasts
- osteocytes
- osteoclasts
What are osteogenic cells?
undifferentiated progenitor cells
Where are osteogenic cells found?
in the deep layers of the periosteum and the bone marrow
What type of cells do osteogenic cells undergo differentiation into?
osteoblasts
What do osteoblasts do?
forming new bone
Where are osteoblasts found?
the growing portions of the bone - endosteum and periosteum
What do osteoblasts do?
synthesise and secrete organic components which surround the osteoblast and calcify it - it then becomes trapped within a matrix and develops into an osteocyte
What are osteocytes?
the primary cells of the mature bone
What are osteoclasts?
the bone cells responsible for breaking down bone
What is different about osteoclasts to other bone cells?
they are not derived from osteogenic progenitor cells, instead a class of macrophages or monocytes
How do osteoclasts break down bone?
they secrete acid or enzyme that break down bone
What is the scientific name for bone formation?
ossification
What tissue does the skeleton develop from?
the embryonic mesenchyme
What is the embryonic mesenchyme?
it is essentially a tissue made up of unspecialised cells in a gel-like matrix which the bones develop from
What are the 2 types of ossification?
- intramembranous ossification
- endochondral ossification
How does intramembranous ossification occur?
- the mesenchymal cells aggregate in sites of bone development
- they then migrate and form small clusters called condensations
- the bone forms directly within the condensation
How does endochondral ossification occur?
the bone is formed on top of a cartilage template, which is then replaced by bone
What are the 2 different types of bone growth?
- appositional (width)
- interstitial (length)
What are the steps of appositional bone growth?
- the periosteum on the outside of the bone has osteoblasts
- the endosteum on the inside lines the marrow cavity and contains osteoclasts which digest bone
- bone is deposited on the outside and resorbed on the inside
- this occurs in balance, so bone increases in thickness and the medullar cavity increases in size
What are the steps of interstitial bone growth?
- occurs at the growth plate
- the growth plate is made of cartilage
- new cartilage is produced at the growth plate and pushes the growth plate towards the epiphyseal seal, lengthening the bone
- the cartilage dies and is replaced by bone cells
- continues until adulthood and the cartilage is fully replaced by bone leaving an epiphyseal line
- the chondrocytes stop dividing so no more growth can occur here
Why is bone remodelling important?
- repairs damaged bone
- important role in calcium homeostasis
What are the stages of bone remodelling?
- in the resting phase, the bone cells are lined with inactive osteoblasts
- a trigger (hormone release or a fracture) activate the cells within the lining of the bone cells
- osteoclasts gather and form a pit in the bone and dissolve it by releasing acid and lysosomal enzymes
- when the bone has been dissolved, the osteoclasts undergo apoptosis
- macrophage like cells remove debris after apoptosis
- osteoblasts can then produce alkaline phosphate to produce osteoid
- the matrix undergoes mineralisation with calcium and phosphorous to form new bone
- continuous process
What is peak bone mass?
when someone’s bones reach peak density and strength
Why do people over 30 experience a gradual loss in bone mass?
decreased activity of osteoblasts
Why do menopausal women experience a reduction in bone mass?
osteoclasts cell death is regulated by oestrogen, so if oestrogen levels decrease, the osteoclasts stay active for longer
What is osteoporosis?
decreased bone mass
What are the 4 main steps of bone repair?
- hematoma formation
- soft callus formation
- hard callus formation
- bone remodelling
What are the steps of hematoma formation?
- blood is released from the damaged blood vessels in the bone
- white blood cells remove dead cells
- osteoclasts remove dead bone fragments
- granulation tissue also forms hyaline cartilage
What are the steps of soft callus formation?
- the cartilage is converted by granulation and becomes revascularised
- this leads to formation of a soft callus
- the soft callus gradually becomes ossified and new bones form
What are the steps of hard callus formation?
- the osteoblasts deposit a temporary bony collar around the cartilage until ossification takes place and the broken pieces are replaced
What are the steps of bone remodelling?
- small bone fragments are removed by the osteoclasts whilst the osteoblasts deposit spongy bone and then convert it to compact bone
define joint
where two or more bones meet allowing movement and structural stability
What are the 3 types of joints?
- synovial joints
- fibrous joints
- cartilaginous joints
What type of movement do synovial joints allow?
free movement
What are the 6 subtypes of synovial joints?
- planar
- hinge
- pivot
- condyloid
- saddle
- ball and socket
What are the main components of a synovial joint?
- synovial membrane
- synovial fluid
- joint capsule
- articular cartilage
- ligaments
What does the articular cartilage do?
covers the ends of the bones to reduce friction
What does the synovial membrane do?
lines the joint cavity and secretes synovial fluid which lubricates the joints
What 2 components is the joint cavity made up of?
the joint capsule and the synovial membrane
What does synovial fluid do?
provides nutrients to the joints and acts as a lubricant
What is the joint capsule?
a fibrous sleeve that encloses the joint to provide protection
What do the ligaments do?
they are connective tissue that stabilise a joint and connect joint to bone
How are the muscles connected to the bone?
by tendons
If joints lack blood vessels, where are nutrients obtained from?
directly from the synovial fluid
What are the 3 main axes that movement occurs along?
- X-axis (side to side)
- Y-axis (up and down movement)
- Z-axis for 3D movement (swinging around arm)
define uniaxial joint
joints that move along a single axis
define biaxial joint
joints that move through 2 distinct axes
define polyaxial joint
joints that can move through all 3 axes
What is osteoarthritis?
when the articular cartilage in the joints breaks down over time
What is rheumatoid arthritis?
an autoimmune condition where the immune system attacks the cells that line the joints
What does rheumatoid arthritis cause?
inflammation and thickening of the synovial membrane and the joint capsule
