Robyn Flashcards
1
Q
What is physiology?
A
‘the science of the functions of living organisms and their parts’
2
Q
What is homeostasis?
A
the maintenance of a steady state to allow optimum bodily function
3
Q
What does negative feedback do?
A
Reverses a change to maintain a normal value
4
Q
What does positive feedback do?
A
Strengthens or reinforces a change
5
Q
What are the life processes?
A
Movement, reproduction, sensitivity, growth, excretion, respiration, nutrition- these processes maintain homeostasis- MRS GREN
6
Q
What levels does physiology allow us to understand?
A
Physiology allows us to study the function of an organism at the molecular, cellular, organ and whole body levels
7
Q
What is pharmacology?
A
study of mechanisms by which drugs affect the function of living systems
8
Q
What is a drug?
A
a chemical substance of known structure, other than a nutrient or an essential dietary ingredient, which, when administered to a living organism, produces a biological effect
9
Q
What is the receptor theory?
A
Receptors are macromolecular protein complexes that serve as recognition sites for neurotransmitter and hormones
Receptor also refer to any component of a cell that can bind a drug, which then modulates some activity of the cell.
10
Q
What is a receptor?
A
Receptors are proteins that recognise and bind specific chemical mediators
11
Q
What is specificity?
A
Different types of receptors exist for each type of chemical mediator
12
Q
What are ligands?
A
They are small molecules e.g. hormones, neurotransmitters, inflammatory mediators that bind receptors
13
Q
What is an agonist?
A
They ‘activate’ receptors, changing cell behaviour
14
Q
What is an antagonist?
A
They prevent ‘activation’ of receptors by agonists
15
Q
What are two types of opiates?
A
Morphine, Heroine
16
Q
What are two types of muscarinic?
A
Pilocarpine, Atropine
17
Q
What are two types of nicotinic?
A
Nicotine, Curare
18
Q
How does pilocarpine and atropine exert its effect? and what’s the conclusion?
A
Pilocarpine slows heart rate
Atropine prevents effects of pilocarpine on heart
Pilocarpine can also induce secretion from salivary glands and atropine stop its affects
conclusion: there is some substance/substances in the nerve endings or gland cells with which atropine and pilocarpine are capable of forming compounds
19
Q
How does nicotine and curare work? what conclusion could be said about them?
A
- Site of action for nicotine is on skeletal muscle
- Nicotine able to induce tonic muscle cells, even when nerves to the limb had been cut ad allowed to degenerate
- Nicotine acts directly on muscle cells rather than paralysing the motor nerve endings
- By injecting curare, nicotine evoked contraction stopped
conclusion: nicotine and curare did not directly act on the muscle but rather on some accessory substance of the muscle cell
20
Q
What is the endocrine system used for?
A
Long distance signalling
21
Q
What is a hormone?
A
A hormone is a chemical mediator that is released in one part of the body but regulates the activity of cells in other parts of the body
22
Q
What are the differences between the endocrine system and the nervous system?
A
Nervous- Chemical or electrical signals, uses neurotransmitters, short distance travelled, fast response time, targets internal and external environment
Endocrine- chemical messengers, hormones, long or short distance, fast or slow, internal environment
23
Q
What does the pineal gland do?
A
Produces melatonin (sleep/wake cycles)
24
Q
What does the pituitary gland do?
A
Produces FSH, oxytocin, growth hormone
locked in with hypothalamus
25
What does the thyroid gland do?
Produces T3 and T4
26
What does the adrenal gland do?
Above kidney
| adrenaline, noradrenaline
27
What does the pancreas do?
Production of insulin and glucagon
28
What do the ovaries do?
They produce progesterone and oestrogen
29
What do the testes do?
They produce testosterone
30
What do exocrine organs do?
Secrete into ducts
31
What do endocrine organs do?
secrete hormones into interstitial fluid surrounding secretory cell. Then carried in the blood around the body
32
What does the parathyroid do?
Secretes PTH which regulates calcium levels
33
Were is the anterior pituitary gland connected to?
The hypothalamus is connected to the anterior lobe of the pituitary gland by means of a special portal blood system
34
What is a portal system like the one that connects the hypothalamus and the anterior pituitary gland?
A capillary bed pooling into another capillary bed through veins, going through the heart
35
How is the hypothalamus connected to the posterior lobe of the pituitary gland?
Hypothalamus is directly connected to the posterior lobe of the pituitary gland by means of neurones
36
Does the hypothalamus regulate the pituitary gland?
Yes it does
37
What are examples of hormones having an effect on their target cells?
Insulin and thyroid hormones- look up the action of these
38
What are the abnormalities of high and low insulin?
Diabetes
39
What are the abnormalities of high and low thyroid hormone levels?
Low-- congenital hypothyroidism
Cretinism-
- Mentally immature, cannot hear or speak
- Bone growth retarded
- Sexually immature
High-- Graves disease
Autoimmune disease- produce antibodies that ‘mimic’ TSH – too much thyroxine- triiodothyronine
- Excessive connective tissue behind eyes – exophthalmos
40
How do insulin and glucagon work?
In a feedback loop
A rise in blood glucose levels causes release of insulin from beta cells in the pancreas, promoting glucose uptake in cells and storage of glycogen in liver and muscles
A fall in blood glucose levels stimulates alpha cells in pancreas to secrete glucagon, which causes liver to break down glycogen into glucose
41
What is the parasympathetic nervous system?
The parasympathetic nervous system is one of the divisions of the autonomic nervous system. Sometimes called the rest and digest system.
42
What is the parasympathetic nervous systems function?
Rest and digest. (taking in food/energy and removing waste products)
Digestion, defecation, and diuresis
Function in a discrete, organ specific manner. doesn’t have the whole-body response because it is not connected to the endocrine system
43
What is the sympathetic nervous system?
The sympathetic nervous system (SNS) is part of the autonomic nervous system (ANS). The sympathetic nervous system activates what is often termed the fight or flight response.
44
What is the function of the sympathetic nervous system
Fight or flight
Exercise (need to increase blood supply to muscles), excitement, emergency, and embarrassment
Can be coordinated, whole body response this is due to the connection to the adrenal medulla and endocrine system
Can be discrete and organ specific
45
What is the autonomic nervous system?
The part of the nervous system responsible for control of the bodily functions not consciously directed, such as breathing, the heartbeat, and digestive processes.
Has two divisions: sympathetic and parasympathetic nervous system
46
Explain sympathetic stimulation
Increased heart rate, cardiac contractility (Not only increasing heart rate but with each pump there is more strength and more blood pumped around) and blood pressure.
Re-direction of blood to skeletal and cardiac muscle:
– Vasoconstriction (constriction of the blood vessels) in viscera
– Vasodilation (increasing diameter of blood vessels) in skeletal muscle & cardiac muscle
– Need to get more glucose and oxygen to the skeletal muscles
Increased ventilation and bronchodilation
- Breathe in more oxygen
- Airways widen which allows more oxygen to enter the lungs
Increased blood glucose levels due to stimulation of glycogenolysis in the liver
Increased break down of triglycerides in adipose tissue to provide fatty acids for increased ATP production
Pupillary dilation
- Give yourself the best possible chance of being able to see where the danger is
47
Explain parasympathetic stimulation
Decreased heart rate and blood pressure
Facilitates digestion and absorption of nutrients by:
– Promoting secretion (including salivation)
– Increasing mobility (including swallowing) of the gastrointestinal tract
Necessary for defecation and urination
Pupillary constriction
48
Describe preganglionic neurons
* Always myelinated
* Always cholinergic fibres i.e. release ACh as their primary neurotransmitter
* Ach crosses the postsynaptic cleft
* ACh activates nicotinic ACh receptors on the postsynaptic cell, receptor subtype is N2
* Ions move in and cause excitation of the postganglionic neuron
49
Receptors and neurotransmitters involved with sympathetic nervous system
* Short, cholinergic preganglionic neurons
* releases adrenaline/noradrenaline
* Long, adrenergic postganglionic neurons
* N2 receptors
* Target tissue expresses α- and β- adrenergic receptors
* Type of receptor mediates what kind of response that happens
50
Diffusion of sympathetic activity in adrenal medulla
* Short, cholinergic preganglionic neurons
* Chromaffin cells function similar to postganglionic neurons but release mainly adrenaline in an endocrine manner (epinephrine). They don’t have an axon
* Adrenalin travels in the blood to multiple tissues and activates them
* Target tissues expresses α- and β- adrenergic receptors
51
What's an exception to the neurotransmitter rule and how does it work
The sweat gland
• Short, cholinergic preganglionic neurons
• Long, cholinergic postganglionic neurons
• Second neuron is also releasing Ach
• Target tissue expresses muscarinic ACh receptors
52
Receptors and neurotransmitters involved with parasympathetic nervous system
* Long, cholinergic preganglionic neurons
* Short, cholinergic postganglionic neurons
* N2 receptor
* Acetylcholine relseased
* Target tissue expresses muscarinic ACh receptors
53
What cranial nerve is involved in parasympathetic outflow?
• The Vagus nerve (cranial nerve X), carries ~80% of total parasympathetic outflow
54
How is the autonomic nervous system controlled by the brain
1. limbic lobe: emotional inputs
2. Hypothalamus: Integrates and co-ordinates ANS functions
3. Brainstem nuclei: E.g nucleus tractus solitarii mediate autonomic reflexes
4. Spinal cord: Mediates autonomic reflexes
Step 3 and 4 essential for autonomic function
55
How can autonomic output be controlled by descending cortical input
* Minimal conscious cortical control BUT cortical processes do regulate autonomic output
* Fear – initiates fight or flight response
* Emotional stress/painful stimuli – can cause vasodilation and hypotension, leading to fainting
* Chronic stress – causes increased gastric acid secretion
* Nervousness – can lead to diarrhoea
56
Describe regulation of ANS by sensory input and gives example
Sensory input from visceral afferent neurons takes priority over cortical functions i.e. nothing else seems to matter
```
Examples
– Hunger
– Nausea
– Bladder and bowel distension
– Hypothermia/hyperthermia
– Visceral pain
```
57
Why do we have a circulatory system?
* An evolutionary consequence of an increase in size and complexity of a multicellular organism
* Provides a steep concentration gradient from the blood to cells for nutrients, and from cells to blood for waste products
58
what are the functions of the circulatory system?
• Primary function:
– distribution of gases and molecules for nutrition, growth and repair
• Secondary functions:
– enables hormonal signalling- adrenaline released by the adrenal medulla won’t be useful
– dissipates heat
– mediates inflammatory and host defence responses
59
Name the three functional parts
– A pump = the heart
– A fluid = the blood
– A set of containers = the blood vessels
60
Describe the systemic circuit
* Parallel pathways from left to right
* Usually flows through a single capillary bed
* Can have two capillary beds in series e.g. kidneys
* Can have capillary beds in parallel and series e.g. spleen, intestines and liver
* Carries blood to all parts of the body except the lungs
61
Describe the pulmonary circuit
* Single pathway from right to left side of heart
* Deoxygenated blood
* Pulmonary artery (only artery which carries deoxygenated blood)
62
Describe the Tunica Interna (Intima)
• Endothelial cells resting on a basement membrane
63
Describe the Tunica Media
* smooth muscle cells
* elastic fibres = elastin core covered by microfibrils
* proportion of smooth muscle cells to elastin fibers varies depending on the type of blood vessel
64
Describe the Tunica Externa (adventitia)
* collagen fibres-
* elastic fibres- allows modulation of the blood vessel and stops it from bursting
* vasa vasorum- blood supply for the blood vessels
* nerves- efferent nerve fibres of the sympathetic nervous system
65
What's varied within blood vessels
* Wall of arteries/arterioles become thicker in relation to lumen size, as the vessels get smaller
* Structural changes in veins with size is less distinct
66
Describe Elastic arteries: large arteries
* High compliance = walls stretch easily without tearing in response to an increase in pressure
* Enables vessels e.g. Aorta to cope with peak ejection pressures
* Makes the flow smoother ensuring the artery does not burst
* Recoil of elastic fibres forces blood to keep moving even when the ventricles are relaxed
67
Describe Muscular arteries: medium-sized arteries
* Smooth muscle cells are arranged circumferentially
* As smooth muscle contracts and gets smaller, it causes constriction
* Capable of greater vasoconstriction and vasodilation to adjust the rate of blood flow
* Vascular tone – state of partial contraction maintains vessel pressure and efficient flow.
68
Describe Arterioles
• Arterioles have smooth muscle enabling regulation of blood flow into capillary networks
• Terminal regions of arterioles are known as metarterioles
• Precapillary sphincters monitor blood flow into the capillary
- Very dense areas
- Capable of cutting off blood supply
69
Regulation of blood flow to capillary networks
Local regulation of precapillary sphincter by metabolites:
•E.g. low oxygen, high CO2, low pH = vasodilation
Extrinsic regulation by the autonomic nervous system:
•Vasoconstriction:
- Noradrenaline activates α1 adrenoceptors
- Noradrenaline released from the postganglionic sympathetic neuron, activates alpha1 adrenoreceptors on smooth muscle cells
•Vasodilation:
- Reduced release of noradrenaline
- Less alpha1 adrenoreceptors activated
70
Describe Capillaries
* Small, terminal vessels composed only of endothelial cells and basement membrane
* Essential for exchange of substances between blood and interstitial fluid
* Three groups based on their degree of leakiness
* nutrients are exchanged via the intracellular junctions
71
Describe venules
* Postcapillary venules are porous and act as exchange sites for nutrients and waste
* Muscular venules have a thin smooth muscle cell layer Less muscular than arterioles
* Thin walls allow expansion and make them excellent reservoirs for blood
72
Describe veins
* Less muscular and elastic but distensible enough to adapt to variations in volume and pressure of blood
* Like venules, veins can “store” blood
73
Describe large veins
•More muscular than venules and smaller veins
•Possess valves to prevent backflow
•Defective, leaky valves allow backflow and can lead to varicose veins
- Build-up of tissue and fluid
74
Why do we need a lymphatic system?
* More filtration than absorption occurs, leaving ~3 L of fluid and ~150 g of protein per day in the interstitial fluid
* This excess fluid and protein enters into lymphatic vessels to form lymph.
* Lymph vessels eventually drain back into the blood, returning the fluid and proteins
75
What are the functions of the lymphatic system
There are three primary functions:
1. Drains excess interstitial fluid, maintaining the circulating volume of blood
2. Transports dietary lipids
3. Carries out immune responses
76
Describe the organisation of the lymphatic system
• 3 basic functional parts:
- Lymph
- Lymphatic vessels
- Lymphatic tissue containing lymphocytes, found in a number of structures and organs
• Diffuse system
- Taking fluid back in from the circulatory system
77
Explain the structure of blood vessel walls and relate directly to their function:
– Arteries can be either elastic or muscular
– Muscular arterioles control blood flow and pressure
– Thin capillary walls allow diffusion of substances
– Veins possess valves to prevent backflow
78
What do the specialised valves of the lymphatic capillaries enable?
The lymphatic system to return excessive fluid and protein filtrate to the circulatory system
79
Describe Lymphatic capillaries/Initial lymphatics
* More leaky than blood capillaries
| * Possess interendothelial junctions called Primary lymph valves
80
Describe Lymphatic vessels/Collecting lymphatics
* Endothelium plus sparse smooth muscle
* Similar to small veins
* Possess secondary lymph valves that restrict backflow
81
Describe the expansion phase
During expansion phase hydrostatic pressure in the interstitium, exceeds that in the initial lymphatic causing microvalves to open and fluid to enter
82
Describe the compression phase
During the compression phase, hydrostatic pressure in the initial lymphatic rises, closing the microvalves and opening the secondary lymph valves, causing fluid to flow downstream
83
Explain the communication between the blood vessels and lymphatic vessels using lymphatic ducts lymphatic vessels, valves and lymph nodes as examples
Lymphatic ducts: empty the lymph into the junction of jugular and subclavian veins of the cardiovascular system
Lymphatic vessels: pass lymph to lymphatic ducts
Valves: ensure one way
Lymph nodes: remove foreign substances through filtering lymph, phagocytosis and immune reactions
84
What is Lymphoedema?
Damage to the lymphatic system that can lead to ineffective drainage and excessive fluid build up
85
What is blood pressure?
The force (or hydrostatic pressure) that blood exerts against a blood vessel wall
86
Why is blood pressure important?
•Blood flow to a given tissue must match the metabolic rate of that tissue
•Without this adequate supply of oxygen and nutrients tissue will start to undergo necrosis
•Haemodynamic, the physical principles of blood flow, are based mainly on:
- Pressure
- Resistance
87
What is Haemodynamics
Relates to the flow of blood within the organs and tissues of the body.
88
The greater the pressure difference between two points...
the greater the flow
89
Where does blood move from
regions of high pressure to regions of low pressure
90
What's the measure of blood pressure?
mmHg (millimeters of mercury)
91
Greater the resistance within the system...
the less the flow
92
What does Vascular resistance (or total peripheral resistance) depend on? and how
- Size of the vessel lumen: only need a small change in radius to get a big change in flow
- Length of the blood vessel: longer the blood vessel, greater the resistance and slower the flow
- Blood velocity:
93
What does blood pressure depend on?
– the system e.g. systemic or pulmonary
– the distance from the ventricle of the heart
– whether the heart is in systole (contraction) or diastole (relaxation)
94
What is Hydrostatic pressure?
a pressure exerted by a liquid in response to an applied force.
95
what causes a higher blood pressure?
Cardiac output from both sides of the heart is equal but total resistance of the systemic circuit is much greater
96
Define systolic pressure, diastolic pressure and pulse pressure?
•Systolic pressure:
– The peak arterial BP attained during ventricular systole (contraction) what detained when ventricle contracted
•Diastolic pressure:
– The minimum arterial pressure during ventricular diastole (relaxation) when ventricles relaxed
•Pulse pressure:
- The difference between systolic and diastolic pressure
97
Define Pulse
Rhythmic pressure oscillation that accompanies each heartbeat
98
What are the determinants of aortic systolic and diastolic blood pressures?
•Systolic pressure is mainly affected by:
- Ejection velocity, EV how quickly blood is ejected from heart
- Stroke volume, SV how much is ejected from the heart
Diastolic pressure is mainly affected by:
- Total Peripheral Resistance
- mostly arteriole resistance
- Blood flow from arterial to venous sides
99
Define Mean arterial pressure (MAP) and what is the equation?
The average blood pressure in arteries
| MAP = diastolic BP + 1/3 (systolic BP – diastolic BP)
100
Pulse pressure equation?
systolic BP – diastolic BP
101
Measurement of arterial BP
* Typically measured in the brachial artery with the arm at heart level
* Measured using a sphygmomanometer and a stethoscope
102
Explain how you would use a sphygmomanometer and a stethoscope to measure arterial blood pressure
1. Inflate cuff to a pressure greater than the person’s systolic BP to prevent any blood flow in the artery
2. Start to slowly deflate the cuff
3. As the cuff deflates, a spurt of blood flows through the artery and a sound is heard = systolic pressure
4. Once the sound becomes softer/muffled = diastolic pressure
103
What are the associated sounds called and what does a loud sound and silence indicate when measuring blood pressure?
* Associated sounds are Korotkoff sounds
* The loud sound is caused by turbulent blood flow
* The silence which resumes indicates that laminar blood flow has resumed
104
Explain local regulation of arterial blood pressure
1. Homeostasis becomes disturbed by: chemical changes, physical stress, increased tissue activity
2. inadequate local BP and blood flow
3. Local decrease in resistance and increase in blood flow
4. Homeostasis normal BP and volume
105
Explain what happens if local regulation of arterial blood pressure is ineffective
1. Local decrease in resistance and increase in blood flow
| 2. Lead to either stimulation of endocrine response or detection by baroreceptors
106
How does stimulation of endocrine response regulate arterial blood pressure?
Long term increase in BP by increasing blood volume
107
How does detection by baroreceptors regulate arterial blood pressure?
1. processed by cardiovascular centre
| 2. short term increase in BP by: increased cardiac output, peripheral vasoconstriction
108
Where do you find baroreceptors?
Carotid sinus found internal and external carotid arteries and aortic arch
109
What do baroreceptors detect?
stretching of vessel wall
110
What are baroreceptors?
Baroreceptors are branched terminals of both myelinated and unmyelinated sensory fibres which are integrated within the elastic layers.
111
What happens when baroreceptors are activated?
As the wall is stretched due to high BP, baroreceptors are activated causing them to have an increase in action potentials. This increase in action potentials flows up into the cardiovascular centres in the medulla
112
Describe short term regulation of arterial BP
* Baroreceptor reflexes are negative feedback loops
* Detectors = baroreceptors
* Integrator = cardiovascular centre
* Efferent neural pathway = autonomic nervous system
* Effectors = cardiac muscle and vascular smooth muscle, which adjust cardiac output and peripheral resistance
113
What are the three basic nuclei in the cardiovascular centres?
Cardioinhibitory, vasomotor, cardio-acceleratory
114
Define Cardioinhibitory centre
- Increases parasympathetic activity to heart
- The centre in the medulla oblongata that gives rise to impulses that decrease the heart rate. Impulses reach the heart by way of the vagus (parasympathetic) nerves.
115
Define Vasomotor centre
controls activity of sympathetic neurons that innervate vascular smooth muscle: When baroreceptors are inhibited the vasomotor centre is stimulated, which sends information via efferent autonomic pathway to cause vasoconstriction
The vasomotor centre (VMC) is a portion of the medulla oblongata that, together with the cardiovascular centre and respiratory centre, regulates blood pressure and other homeostatic processes.
116
Define Cardio-acceleratory centre
increases sympathetic activity to heart- increase cardiac output via increasing heart rate and increasing cardiac contractility.
117
What are baroreceptors reflex loops?
negative feedback loops
118
What does an increase in sympathetic output and decrease in parasympathetic output lead to?
increase cardiac output and blood pressure increasing
119
Example of when you need short term regulation of arterial BP?
During orthostasis
120
Define orthostasis
Orthostatic hypotension, also known as postural hypotension, occurs when a person's blood pressure falls when suddenly standing up from a lying or sitting position
121
What happens when you stand up too quickly?
Blood drains from your upper body, baroreceptor are inhibited as a decrease in pressure and blood vessels less stretched
Because of this response in medulla which causes cardiac centre to accelerate heart rate and cardiac output and restores balance quickly
122
Define Long term regulation of arterial BP
- hormonal response
- Negative feedback loops
- Adjusts blood volume
123
When a drop in blood pressure cannot be rectified by the neural response, what response kicks in?
the kidneys response
124
What hormone is release into the blood stream once the low BP has been detected by kidneys and how does this return to normal BP
1. Renin is released into blood stream.
2. Renin converts an enzyme called angiotensinogen (protein made in the liver) into angiotensin 1,
3. Angiotensin 1 is further converted into angiotensin 2, this is done by removing two amino acids, done by angiotensin converting enzyme ACE
4. Angiotensin 2 flows up to hypothalamus flowing through and stimulating certain cells which tell you to increase the amount of fluid you’re taking in, causing you to become thirsty
5. As you drink more, will become absorbed in digestive system and increase your blood volume and therefore increase pressure
125
What are the effects of angiotensin 2?
Angiotensin2 can also act directly on blood vessels causing vasoconstriction, increasing blood pressure
Angiotensin 2 also acts back on the adrenal cortex causing it to release aldosterone
126
A pathological variation in BP
Hypertension
127
What is hypertension?
a chronic resting blood pressure > 140/90
128
Name and explain drugs that disrupt the renin-angiotensin-aldosterone system:
- Angiotensin converting enzyme (ACE) inhibitors
E.g. Ramipril
Inhibitor conversion of angiotensin one to angiotensin two, prevents the effects of angiotensin 2
- Angiotensin receptor blocker (ARB)
E.g. Losartan
Allow angiotensin 2 to be produced but has no effect on tissues, blocks receptors it normally works on.
All the effectors it works on has to have a receptor present, so angiotensin receptor would be present in the hypothalamus, adrenal cortex and blood vessels
If receptor is blocked, angiotensin 2 would have no effect
129
Name and explain a drug that reduces blood volume:
- E.g. Thiazide diuretics
Give a diuretic- give something that makes you lose more water through your kidneys
More water lost through kidneys, blood volume would decrease meaning blood pressure would decrease
130
name and explain drugs that decrease cardiac output:
- Sympathetic 1 adrenoceptor antagonist
- E.g. Metoprolol
Works by binding to beta 1 adrenal receptors
Have an antagonist that fights against the noradrenaline for binding to the beta 1 adrenal receptors, if we have a competitive antagonist you get less binding of the noradrenaline to receptor which means you get less effect
Less sympathetic effect, you don’t get as large increase in heart rate and as large increase in contractility
131
name and explain drugs that decrease total peripheral resistance via vasodilation:
- Sympathetic α1 adrenoceptor antagonist
E.g. Doxazosin: If we have an antagonist for Alpha one adrenal receptor then noradrenaline won’t have as an big effect, smooth muscle cells wont be as contracted
- Calcium channel antagonist
E.g. Nifedipine: decrease smooth muscle contraction, still allowing noradrenaline to signal to the smooth muscles to contract but, for smooth muscle to contract they need calcium to move into the cells
So, prevent calcium from moving into cells
132
What does the gastrointestinal tract provide?
water, electrolytes, vitamins and nutrients
133
What is the gastrointestinal tract designed to do?
smash up food both physically and chemically, so it may be absorbed together with water
134
What does the Buccal cavity do?
mechanically breakdown food with teeth, maxilla, turn food into smaller particles with increased surface area, mix with saliva which provide lubrication
135
What's the function of buccal cavity?
Mastication
• Teeth and tongue mechanically break down food and the addition of saliva, results in a smooth soft bolus of food, lubricated and readily swallowed
• muscles of mastication are masseter, temporalis, and the pterygoids- innervated by V3 of trigeminal (CNV)
• Saliva contains alpha-amylase which begins breaking down starches in the bolus.
• Some people have more than other
• Digestion begins in the mouth
136
Describe the Oesophagus
Conduit between orophyaynx and stomach
Fibromuscular tube about 20-25cm long
Passes posterior to the trachea and the heart,
pierces the diaphragm and enters the fundus of the stomach.
Consists of layers of muscles, mucosa (inner lining), submucosa and connective tissue
Muscular layer preforms peristaltic movements to push the bolus of food down into the stomach
137
Function of the Oesophagus and what controls entry into it
conveys food from mouth to stomach- upper sphincter controls entry into oesophagus
138
Describe the Stomach
Bag-like, dilated section of the GI tract which can hold about 1 litre of food.
Lies in upper left of abdominal cavity, against the diaphragm
Releases proteases an HCl, former begins smashing up proteins, the latter
is bactericidal.
Stomach churns its contents through peristalsis producing chyme in 40-60 mins
Stomach releases the chyme, in small quantities, into the duodenum through the pylorus sphincter – pylorus acts as a pump
churns through peristalsis
139
Describe the duodenum
The duodenum is a 25–38 cm C-shaped structure lying adjacent to the stomach
Enzymatic breakdown of chyme occurs in duodenum
Four distinct sections, each with its own distinct function
Duodenum regulates the control of stomach emptying via hormones-secretin and
Cholecystokinin
Four regions with slightly different functions
When food goes into duodenum, cholecystokinin is released which stops pyloric area of the stomach from contracting and therefore closing it up. – so it can regulate how quickly food goes in and out the duodenum
140
Main role of duodenum
bulk of digestion. digestive enzymes and intestinal juice secreted
141
Jejunum/Ileum main role
- digestive enzymes from pancreas and liver enter via pancreatic duct
- where absorption starts to happen, digestive juices secreted from pancreas and liver
142
function of Jejunum
* Much absorption occurs here
* Inner surface consists of finger-like villi projections which increase the surface area of the jejunum allowing or greater absorption of nutrients. pH = > 7
* Villi epithelium is a ‘brush border’ made up of microvilli increased surface area
* Nutrient transport across epithelial cells is passive for sugar fructose, passively transported but active for amino acids, small peptides, vitamins, and most glucose. They are actively transported
Villi have blood supply so when absorbed nutrients has a direct pathway
Some juices secreted by the duodenum and jejunum are alkaline, which neutralise the acid contents of the stomach and therefore make it more alkaline. This is because the enzymes in the jejunum prefer higher pH to function properly
143
Ileum function
Subtle differences between jejunum and ileum
The diameter of its lumen is smaller and has thinner walls than the jejunum
The ileum has more fat inside the mesentery than the jejunum
Abundant Peyer's patches, encapsulated lymphoid nodules that contain large
numbers cells of the immune system.
Absorbs vitamin B12, bile salts and products of digestion not absorbed by the jejunum
Mesentery: a membrane that tethers the GI tract to the abdomen
Peyers patches: encapsulated lymphoid nodules- part of lymphatic system
144
Large Intestine (Colon) function
Three functions:
• Absorb the remaining water and electrolytes from indigestible food matter;
• Accept and stores food remains that were not digested in the small intestine;
• Eliminate solid waste (faeces) from the body.
Four parts of the colon: Ascending colon, transverse colon, descending colon, sigmoid colon
Indigestible food is absorbed- anything left over
Important for the absorption of water and electrolytes
145
Main role of Caecum
absorbs fluids and salts remaining after intestinal digestion. mixes with mucus
146
Caecum function
Pouch-like structure that is considered to be the beginning of the large intestine
The ileum pushes chyme into it through the ileo-caecal valve
Larger in herbivorous animals where cellulose-digesting bacteria are house(humans cannot digest cellulose as we do not have these enzymes)
Smaller or even absent on carnivorous animals and replaced by the appendix
Ileo-caecal valve opens up to allow indigestible products into the caecum, if full will be slowed down
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Main role of Rectum
Electrolytes/water absorbed. faeces thickened and mucus added
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Rectum function
* Temporary store for faeces
* The final part of the large intestine connecting to the anus
* The rectum approximately follows the shape of the sacrum.
* The end expands into the rectal ampulla where faeces is stored before defaecation
* Stretching of rectal walls stimulates stretch receptors and causes the desire to defaecate.
* Voluntary retention of faeces pushes it back into the colon where more water will be extracted, making it harder and may lead to constipation.
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Main role of anal canal
continence organ. regulates defaecation. lubricates and transmits faeces from rectum to outside world
150
What's involved in the upper GI tract?
Buccal cavity
Oesophagus/oropharynx
Stomach
duodenum
Involved in smashing up food
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What's involved in the small intestine?
duodenum
Jejunum
Ileum
Nutrients and water reabsorption
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what's involved in the lower GI tract?
Caecum
rectum
anal canal
water and electrolyte reabsorption and elimination
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What is mastication?
Chewing or mastication is the process by which food is crushed and ground by teeth.
154
why do we chew?
Fruit and veg which have indigestible cellulose walls around the nutritious bits
Enzymes work on surface of food particles so smaller particles therefore, larger surface area: volume ratio
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Chewing reflex
1. Presence of bolus in the mouth initiates reflex inhibition of the muscle of mastication- mandible drops
2. This initiates a stretch reflex of the muscles of mastication that leads to rebound contraction and elevation of mandible and closure of the teeth
3. This compresses the bolus against the lining of the mouth which inhibits the muscles of mastication once again allowing the mandible to drop and rebound another time
156
Describe Primary peristalsis
Continuation of peristaltic wave that commences in oropharynx and spreads to oesophagus.
Pharynx to stomach- 8-10 seconds.
Gravity assist = 5-8 seconds
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Describe Secondary Peristalsis
sweeps down any remaining food
Trigger is distension of oesophagus Peristaltic waves of skeletal muscle controlled skeletal nerve impulses from CNIX and CNX
Smooth muscle controlled by CNX
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Name a disease of the Oesophagus, symptoms and management
* Barrett’s Oesophagus
* Metaplasia (abnormal change) of cells lining the lower oesophagus
* Exposure to stomach acid in in reflux oesophagitis: The normal stratified squamous epithelium is replaces by simple columnar epithelium with goblet cells (lower GIT cells).
Symptoms-
- Heartburn
- Dysphagia
- Haemtemesis
- Sub-sternal pain
- Erosion of teeth due to acid exposure
• Management: proton pump inhibitor, endoscopic surveillance, resection of the oesophagus
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How does the stomach work?
Food enters the stomach and forms concentric circles in the orad portion of the stomach-old food by wall, newest food by opening of oesophagus
Food stretches the stomach and a vagovagal reflex from the stomach to the brainstem and back to the stomach
Reducing the muscular tone and allowing the stomach to bulge outwards and accommodate more food.
To a maximum of 0.8-1.5L
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What secretes gastric juices?
Gastric gland
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How does food move from stomach into the duodenum
1. Pylorus is slightly tonically contracted thus acting as a sphincter
2. Open enough to allows fluids to pass directly into duodenum
3. But prevents food particles passing until they are well mixed and fluid-like
4. Opening and closing of the pylorus is controlled by nervous and hormonal signals sent by stomach and duodenum
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How is stomach emptying controlled
The duodenum provides the most potent signals for stomach emptying
Rate is never greater than the rate the chyme can be digested and absorbed in the small intestine
Duodenum and stomach work together- send signal to each other
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Name Factors increasing rate of stomach emptying
- Increase food volume in the stomach-stretches the walls eliciting ‘myenteric reflexes’
- Gastrin- hormone produced by G-cells in the antral mucosa: Mainly causes production of highly acidic gastric juice
- Also, mild stimulatory effects on motor activity of ‘pyloric pump
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Name factors that decrease rate of stomach emptying by the stretch of the duodenum
Directly inhibits pyloric pump via enteric nervous system in gut wall
Via extrinsic nerves
- prevertebral, sympathetic ganglia
- back to stomach via inhibitory sympathetic fibres
Vagus nerves to brainstem
- inhibit excitatory signals to the stomach through the vagi
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Peptic Ulcer: causes, symptoms, treatment
Damage to the wall of the stomach by stomach acid
-Symptoms are gnawing, burning, upper abdo pain that worsens on eating (secreting more acid), Indigestion ‘heartburn’, nausea
Causes:
- Helicobactor pylori 60% of gastric and up to 50–75% of duodenal ulcers.
- Causes chronic inflammation in the antral mucosa.
- Acid secretion leads to erosion of the gastric wall
- Non-steroidal anti-inflamatory drug such as ibuprofen or aspirin –long time or at high doses
Treatment:
- Proton Pump Inhibitor (PPI)- reduces acid to near zero allowing ulcer to heal naturally
- ‘Triple therapy’ if caused by H.pylori- amoxicillin, clarithromycin and PPI
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Gastric Cancer: Symptoms, causes
Develops from lining of the stomach, average age of diagnosis = 69 years
```
Symptoms:
Pain or buring sensation on swallowing
Food may stick in throat or chest
Weight loss
Upper abdominal pain
Persistent dyspepsia and burping
Feeling full after even small amounts
Nausea and vomiting
Bleeding (-> dark stools), tiredness
and breathlessness
```
causes:
All the usual bad things bad diet, smoking etc
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How is the GI tract specialised for absorption of nutrients and water
- Folds of Kerckring: Folds that increase the absorptive surface area by 3 times- well developed in duodenum and jejunem protruding 8mm into lumen
- Villi-project from the very surface of the mucosa by 1mm.
- Numbers decrease toward distal end of the GI tract.
- Microvilli- each epithelial cell has many 1000s of 1µm extensions-brush border.
- 20 fold increase in surface area!
- Overall- 1000-fold increase in surface area …250m2(in small intestines alone)
- Ingested fluid = 1.5L. Gastro secretions = 7L therefore 8-9L absorbed each day
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How is water reabsorbed?
- Transported entirely by diffusion going from high low concentrations.
- If chyme is dilute enough, water absorbed from mucus villi to blood entirely by osmosis
- Can also go in other direction if chyme is hyperosmotic
- but within minutes chyme will be diluted to make it isosmotic with plasma
- Mostly occurs at tight junctions between apical borders of epithelial cells (‘paracellular route’) but also through cells (transcellular route’)
- Osmotic movement of water creates flow of fluid into and through the paracellular spaces and into the blood of the villus
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How are ions reabsorbed?
- Na is actively transported across the intestinal membrane
- 20-30g Na secreted in intestinal secretions/day.
- Less than 0.5% of intestinal Na is lost in faeces since it is rapidly absorbed through intestinal mucosa
- If significant amounts of intestinal secretions are lost to the exterior (diarrhoea), Na reserves can be depleted to lethal levels in hours.
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What chyme is hyperosmotic, how does water flow into interstitial fluid?
The protein transporters co-transport water. Glucose molecules are surround by water this its transported ‘uphill’!
171
How are nutrients reabsorbed?
- Monosaccharides are absorbed by secondary active transport processes
- Final digestion products are monosaccharides glucose 80% and galatose (from milk) and fructose (20%)
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How does Sodium co-transport Mechanism move other substances with it?
1. Active transport of Na+ thru basolateral membrane into interstitial
fluid this depletes Na+ inside the epithelial cell
2. Na+ from the intestinal lumen enters the cell by combining with a transport protein. This protein will not move the Na+ in unless some other substance combines with it. Na+ and and other substance both transported into the cell.
3. Once inside the epithelial cell other transport proteins and enzymes facilitate diffusion of substance through basolateral membrane, into paracellular space and into the blood.
Na and proteins, tri- and dipeptides and amino acids are co-transported with Na.
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How are fats absorbed?
- Broken down into monoglycerides (MG) and free fatty acids (FFA)
- These are first emulsified by the liver secretion, bile, into tiny,3-6nm bile micelles
- Highly charged exterior means they are soluble in chyme
- Micelles carried to the brush border of the epithelial cells and penetrate the recesses in between the agitating microvilli.
- Here the monoglycerides and free fatty acids diffuse out of the micelle and into the interior of the epithelial cell (cell membrane is a phospholipid bilayer!). Micelle remains in chyme and emulsifies more fats acting as a ‘ferry’.
- MG and FFA taken up by smooth endoplasmic reticulum, converted into triglycerides and released to form chylomicrons through the basolateral membrane, up through the thoracic lymph duct and emptied to the blood
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What does the presence of fats in the small intestine cause?
cause it to release cholecystokinin (CCK) which causes the gall bladder to contract and squirt bile into the small insteine to emulsify the fats.
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How does bile emulsify fats?
Bile has hydrophobic and hydrophilic portion
Bile salts will orientate themselves so fat droplet is completely surrounded by the bile salts- makes fat behave like they are soluble
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Absorption of Glucose and galactose?
Secondary active transport(Na)
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Absorption of fructose?
Facilitated diffusion
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Absorption of amino acids
Secondary active co-transport (Na)
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Absorption of peptides
Secondary active co-transport (H)
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Absorption of micelles
Diffusion
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What are peyers patches?
area which allow substances enter to allow immune system to sample what’s going through in case it needs to produce any antibodies
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How does the release of Aldosterone enhance absorption of Na+
When dehydrated, large amounts of aldosterone are secreted by the cortices of the adrenal glands
Within 1-3hrs, increased activation of enzyme and transport mechanisms for Na+ absorption by intestinal epithelium which leads to increased Cl- and water absorption
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Colon motility
Segmented contractions 99% of the time
1. Retain material in the proximal colon (water reabsorption and fermentation)
2. Mixing contents
Colon infested with bacteria which don’t want to get into peritneal
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Main functions of large intestine
High Mucus secretion- goblet cell
No carrier mediated transport of nutrients (absorption by diffusion)
Efficient water reabsorption
Follows Cl and Na movement
HCO3 buffers acid produced by bacterial fermentation
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The composition of faeces
```
10-20% fat
Undigested roughage 30%
10-20% inorganic matter
½ water
3% protein
¼ solid matter
30% dead matter
```
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What are the three main fates for nutrients?
Supply Energy– eg for muscle contraction, maintaining body temperature, active transport, DNA replication, etc
Provide Building blocks– eg for complex molecules such as muscle proteins, cell membranes, DNA, hormones, enzymes, etc
Stored for the future – glycogen in muscle and liver, triglyceride in adipose tissue (brown fat)
Evolutionary advantage versus obesity epidemic
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what are the main dietary components?
* Proteins - essential for growth and repair of body tissues cell, especially muscle
* Fats - an energy source and a valuable source of fat-soluble vitamins, brain and cell wall construction
* Carbohydrates - our bodies' main source of energy essential for brain metabolism
* Minerals - inorganic elements necessary to normal body processes
* Vitamins - play an important part in many chemical processes in the body.
* Water - essential to our normal body function with 60% of the human body made up of it.
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Which fatty acids need to be obtained through diet?
linoleic acid, linolenic acid, arachidonic acid
189
Which amino acids need to be obtained from diet?
histidine, isoleucine, leucine, tryptophan, lysine, methionine, phenylalanine, threonine, valine
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What is our daily calorific intake?
57 % Carbohydrates (bread, potatoes, fruit, cereals)
30 % Fats (dairy products, oils)
13 % Protein (Soy, pulses, beans, yogurt, eggs, meat, poultry, fish)
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Explain the role of the liver?
Liver monitors blood glucose and as it begins to drop, it converts stored glycogen into usable glucose
Rate of change of glucose levels detected not how much is present in blood
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Name a hypothalamic cell and what are they sensitive to?
Glucoreceptors are sensitive to a drop in blood glucose- ’
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Discuss receptors in the stomach that tell us when we are becoming full
Stretch Receptors in wall of stomach- say when approaching being full
Chemoreceptors sensitive to Small amounts of food dissolved in fluid in stomach-send signals to brain
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what hormone is released in the Duodenum (small intestine) and what causes it to be released?
Hormone cholecystokinin- CCK released from mucosal cell layer of duodenum- says ‘stop eating
Food going into duodenum from pyoral sphincter which causes the CCK hormone to be released
195
Name three points about fat cells
1. Fat is longer term energy store
2. Slower to use
3. More energy per unit mass than glycogen
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What is adipose tissue and what protein does this release? and what detects this protein?
'brown fat’ which releases leptin into bloodstream.
| Hypothalamic receptors detect leptin which may be message “plenty of fat in storage-don’t eat anymore”
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what is Hypothalamic Control Centres for?
Control centre for appetite
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What switches does the hypothalamus contain?
‘on’ and ‘off’ switch for feeding
On = lateral region of hypothalamus
Off = ventromedial region of hypothalamus
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The Dual Centre Hypothesis
Theory has fallen out of favour over last few decades- far too simplistic.
Neuropeptide Y-potent stimulator of appetite-but actions are outside hypothalamus.
Thus, hypothalamus can’t be the ‘centre’ of appetite control.
200
What causes damage to parasympathetic system and leads to a vicious cycle of insulin
Ventromedial lesions to hypothalamus
1. blood glucose falls so animal eats more
2. food converted into adipose tissue rather than glucose - animal stays hungry
3. Animal eats more and gets fatter
4. More insulin secreted
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What peptide increases food intake and what produces it?
Ghrelin, produced by stomach cells
202
what peptide decreases food intake and what produces it?
PYY3-36, produced by intestinal cells
203
Discuss what PYY3-36 is and the effects of it
- A potent inhibitor of appetite
- Selectively inhibits appetite-stimulating neurones by binding to receptors called NPY Y2.PYY3-36
- Hormone of satiety- it makes you feel satisfied with the amount you’ve eaten and so you stop
* Effects of PYY3-36 persist for 24hrs )
* The more calories you eat, the bigger rise in PYY3-36
* Slowly digested food (fat and high fibre foods) give bigger rise
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When are ghrelin levels most high?
just before you eat
205
Name functions of skeletal muscles
* Produce movement of body parts: simple motion or coordinated movement.
* Support soft tissues: support the weight and shield visceral organs.
* Maintain posture and body position allows standing position.
* Communication: speech, expression & writing
* Control of openings and passageways: voluntary control of movements of digestive and urinary tracts.
* Maintain body temperature: heat released through muscle contraction participates in control of body temperature.
206
What are the Universal characteristics of muscles
• Responsiveness (excitability)
– capable of response to chemical signals, stretch or other signals & responding with electrical changes across the plasma membrane
• Conductivity
– local electrical change triggers a wave of excitation that travels along the muscle fiber
• Contractility -- shortens when stimulated
• Extensibility -- capable of being stretched
• Elasticity -- returns to its original resting length after being stretched
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What is the basic muscle fibre structure
Myofibrils are composed of smaller structures called myofilaments. There are two main types of myofilaments: thick filaments and thin filaments. Thick filaments are composed of the protein myosin. The primary component of thin filaments is the protein actin.
The thick and thin filaments alternate with each other in a structure called a sarcomere. The sarcomere is the unit of contraction in a muscle cell.
208
How does Contraction ouccur? the sliding of thick and thin filaments
1. ATP binds to myosin head, causing the dissociation of the actin-myosin complex
2. ATP is hydrolysed, causing the myosin heads to return to their resting conformation
3. A cross-bridge forms and a myosin head binds to a new position on actin
4. Pi is released. Myosin heads change conformation, resulting in the power stroke. The filaments slide past each other
5. ADP released
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How is contraction initiated?
1. Nerve impulse reaches the nerve terminal, the neuromuscular junction. Ca2+ is released and causes release of Acetylcholine by exocytosis.
2. Binding of Ach to its receptor causes entry of Na+ into the sarcoplasm, which produces an action potential.
3. Ca2+ is released and binds to troponin, provoking a conformation change that unmasks myosin binding sites.
4. Myosin heads slide along the actin filament, a process that require energy (ATP).
5. The process terminates when nerve impulse stops. Ach is then degraded by Acetylcholinesterase, and Ca2+ is reabsorbed by the sarcoplasmic reticulum. Ca2+ detached from troponin, which returns to its initial position, masking myosin binding sites
210
What is critical to muscle contraction?
Neuromuscular junction - no contraction without impulse
211
What does Botulinum toxin (botulism) lead to and what are its symptoms?
* most common cause of food poisoning
* muscle weakness, paralysis leading to death
* endoproteinase that cleave proteins required for exocytosis of Ach in autonomic nervous system
* 1st symptoms: dry mouth, double vision
* 2nd symptoms: gastrointestinal (diarrhea, vomiting)
* 3rd symptoms: paralysis of limbs, respiratory muscles
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What's the Clinical use of botulinum toxin?
* Treatment of strabismus (cross eyedness) by injection into peri-ocular muscles
* Blepharospasm (uncontrolled eyelid movements)
* Cosmetic treatments (Botox: Toxin A)
213
Properties of slow oxidative muscle fibres
```
Fatigue resistant
Oxidative
Low glycogen content
Aerobic respiration
High quantities of mitochondria
Present in soleus muscle
```
214
Properties of fast Glycolytic (IIb) muscle fibres
```
Fatigable
White
Glycolytic
High glycogen content
Anaerobic respiration
Fewer mitochondria
Present in biceps branchii muscles
```
215
Slow versus fast muscle fibres
* Slow fibers are half the diameter of fast fibers take longer to contract after nerve stimulation
* Fast fibers take 10msec or less to contract
216
What can toxins block and be used to treat?
can block neuromuscular junction function, but can also be used as drugs to treat neuromuscular disorders.
217
What metabolism do slow fibres use and what does that result in?
Aerobic metabolism, which results in the net production of 38 ATP. They are fatigue resistant
218
What metabolism do fast fibres use and what does the result in?
Anaerobic metabolism, which results in the net production of 2 ATP and lactic acid. Fatigue strikes rapidly.
219
What occurs to reduce fatigue in fast fibres?
ATP production occurs through P-creatine hydrolysis
220
Properties of Aerobic exercise
* Typically is a sustained, low level exercise (jogging, distance swimming)
* Stimulation of slow fibers
* Conversion IIb into fast IIa
* Increased fatigue resistance, blood capillaries. No change in muscle strength.
221
Describe Muscle metabolism in Anaerobic conditions
• Glycolytic metabolism (peak activity, fast fibers)
- Advantage: produces ATP in the absence of O2
- Disadvantage: ATP yield is low and toxic products are generated.
222
Describe the cycle of Phosphocreatine, an essential shuttle of ATP
* Creatine is ingested from the diet and transported to muscles via bloodstream.
* 95% of creatine is present in muscles as P-creatine (60%) or creatine (40%).
* The enzyme catalysing the synthesis and degradation of P-creatine is creatine kinase (CK). CK has cytoplasmic and mitochondrial isoforms.
* Provides a readily source of energy in the first minutes of intense exercise.
* Creatine is recycled into P-creatine in mitochondria at rest.
223
When does Fatigue occur?
Muscle fatigue is the progressive weakness of muscle contraction until no response. It strikes when:
* ATP synthesis decreases due to shortage of glycogen (aerobic conditions).
* Lactic acid levels rise and lower the pH of sarcoplasm, which prevents normal functioning of muscles (anaerobic conditions).
* Failure from motor neurons (production of Ach due to reduced availability of Ca2+.)
224
What are the functions of the integumentary system?
* Largest organ in the body: 12-15% body weight and 1.6 to 1.8m2 of surface area.
* Protection: against impact, chemicals, infection…
* Temperature maintenance: regulates heat gain and loss
* Synthesis and storage of nutrient: vitamin D3 synthesis
* Sensory reception: the skin contains receptors that relay information to the nervous system.
* Excretion and secretion: excretes salt, water; secrete milk (mammary glands).
225
Give an overview of the Integumentary System
* consists of skin + accessory structures
* Skin has 3 layers: Epidermis, Dermis, Hypodermis
* Accessory structures are: Glands (2 sweat glands, sebaceous gland), Hair, Nails.
226
What the structure of Epidermis (skin)?
* 2 types of skin: thick skin and thin skin
* Thick skin: palm of hands and feet, no hair, 5 layers (called stratum)
* Thin skin: rest of the body, 4 layers
* Stratified, squamous, keratinized epithelium
227
What's the Life cycle of keratinocytes
• Self-regeneration throughout life.
• 2-4 weeks to complete process.
• Keratinocytes are born in the lower layer
and migrate upward during their life.
higher proliferated
spend lifetime dividing
228
Describe the Stratum Basale and its components
• 3 cell types: keratinocytes, melanocytes, tactile cells
- Keratinocytes are mitotic, are the majority.
- Melanocytes (produce pigment) are responsible for skin colour.
• Eumelanin: brown insoluble pigment
• Pheomelanin: red soluble pigment
- Tactile (or Merkel) cells are connected to sensory nerves and participate to the sense of touch.
229
Describe the Stratum Spinosum and its components
• Thickest layer of epidermis, contains keratinocytes and up to 800 dendritic (langerhans) cells per mm2
- Keratinocytes: are still mitotic, especially the deeper ones. Cells at the surface of this layer have more flattened shape.
- Higher content in keratin.
- Cells detach from the basement membrane, and migrate upward.
Now detached from basement membrane
As move upward they start differentiating
As differentiate start producing keratin
Dendritic cells: Langerhans- important for fighting infection
230
Describe the Stratum Granulosum and its components
• Last layer of the epidermis to have cells containing nuclei
- Contains 3-5 layers of flat keratinocytes.
- Keratinocytes are post-mitotic, make large amount of Keratin and a Glycolipid.
- Keratin forms filaments that are durable.
- Glycolipid spreads over keratinocytes and make the skin water-resistant. Also creates a barrier between upper and lower layers.
Cells rich and compact with granules which contain glycolipids
231
State components of Stratum Lucidum
- Keratinocytes are densely packed, contain no nuclei or organelles.
232
State components of Stratum Corneum
- 15-30 layers of dead, keratinized cells.
- High lipid content permeability barrier.
- Cells at the surface flake off.
233
State the 5 layers of the stratum
basale, spinosum, granulosum, lucidum, corneum.
234
State the 5 stratum of the epidermis
basale, spinosum, granulosum, lucidum, corneum.
235
State properties of the Dermis
- Thicker than epidermis
- Irregular
- 2 layers
- Accessory structures
- Blood vessels, sensory nerves, muscles Dermal papilla
236
Describe the Papillary layer
made of connective tissue. Interdigitates with epidermis.
237
Describe the Reticular layer
irregular, dense connective tissue rich in collagen
238
Describe the Hypodermis
• Also called subcutaneous layer, consists of connective tissue with adipocytes (fat cells)
- Adipocytes: provide protective layer in babies (“baby fat”). In adults, subcutaneous fat is restricted to specific area of the body
Protective against heat loss
239
Name Accessory structures and give some examples
* Hair, nails
* Cutaneous glands: mammary glands, ceruminous glands, sebaceous glands, sweats glands.
- Sweat glands: apocrine and merocrine sweat glands.
- Apocrine glands: secrete product into hair follicles of armpits. Secrete sweat
240
State properties of Merocrine (eccrine) glands
- 2-5 millions
- secrete perspiration: 99% water
- 500ml per day in normal conditions.
- 1 l per hour under exercise
- Thermoregulation
241
What happens when body temperature increases?
- thermostat in hypothalamus activates cooling mechanisms
- Skin blood vessels dilate
- sweat glands activated
242
What happens when body temperature decreases?
- thermostat in hypothalamus activates warming mechanisms
- skeletal muscle activated (shivering)
- skin blood vessel constrict
243
How does Skin act as a barrier
• inside-out barrier (water loss) and outside-in barrier (
infections).
- Physical barrier: toughness of keratin prevents entry of infectious agents (exceptions: cuts, burns, vectors).
- Biochemical barrier: sebum contains bactericidal substances and sweat brings the pH 4-6 (unfavourable to bacteria growth)
- Immunological barrier: Langerhans cells in epidermis (stratum spinosum) trigger immunological response if infection.
244
Synthesis of vitamin D3 by the skin
synthesized in stratum Basale and spinosum, further processed in the liver and kidneys to produce the cofactor of VDR that acts as a transcription factor.
