Histology ๐Ÿ‘ฉโ€๐Ÿ”ฌ Flashcards

1
Q

Outline simple columnar epithelia

A

Taller than wide
Oval nucleus with longer parts adjacent to the longer sides of the cell
Often either have cilia (resp tract) or microvilli (gut erythrocytes)

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2
Q

Outline intestinal epithelium

A

Enterocytes interspersed with goblet cells
More goblet cells in large intestine than small intestine
Brush border of microvilli

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3
Q

Microvilli- what, why, make up, where

A

Projections from columnar cells
Canโ€™t see them individually but seen as a brush border
Increased SA for absorption
Glycocalyx on outer surface
Found on most epithelial cells esp. on absorptive ones e.g in gut + kidney
Contain actin and myosin filaments

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4
Q

Ciliated epithelium- where, how many per cell and what does it do

A
  • Lines nose, larynx +bronchial tree w goblet cells
  • 300ish cilia per cell, help move mucus to the throat after it has trapped inhaled particles
  • Also found in the fallopian tube to transport the ovum
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5
Q

Outline cuboidal epithelium

A
  • Square in profile with a round nucleus
  • Rarely over 2 layers of cells
  • Occur in the ducts of glands e.g sweat and salivary and the pancreas
  • Form much of nephron in the kidney
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6
Q

Outline squamous epithelia

A
  • Single layer
  • Surrounds most thor +abd organs (aka serosa)
  • Also lines pleural and peritoneal cavities
  • Flattened cells
  • Kept moist by watery (serous) extrudate -> lubes it so organs can slide over each other
  • If destroyed organs can stick together forming adhesions
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7
Q

Outline compound (stratified) epithelia

A
  • Multi layered
  • Found in wear and tear situations
  • Most common is stratified squamous
  • Keratinised form forms epidermal layer of skin
  • Cells replaced from stem cells in basal layer of tissue
  • Cells discarded when they reach the top layer
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8
Q

Outline the layers of keratinising stratified squamous epithelium

A
  • Lower layers similar to moist stratified
  • Upper layers synthesise proteins which interacts with cytoskeleton to produce keratin
  • Once filled with keratin the upper layers die off
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9
Q

Outline Pseudo-stratified epithelium

A
  • Appears stratified but is more like simple epithelium
  • Appears multi-layered but is actually single layered when stretched
  • Lines trachea + bronchi allowing for expansion in inspiration (also in urothelium)
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10
Q

Outline cell junctions

A
  • Cells have to be tightly joined together to act as barriers so macromolecules +/or fluids canโ€™t go past
  • 3 typed of cell-cell contact: Desmosomes, tight (adherent) junctions and gap junctions
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11
Q

Outline epithelia

A
  • One or more sheet of cells resting on basement membrane
  • For protection, absorption and secretion
  • Simple - single layer
  • Stratified - 2 or more layers
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12
Q

How does cilia move?

A

Using tubulin and dynein

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13
Q

What is basement membrane mostly made up of?

A

Type 4 collagen

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14
Q

What do desmosomes do?

A

Bind cells to eachother

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15
Q

What do hemidesmosomes do?

A

Bind cells to the basement membrane

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16
Q

What are the 3 types of cell junctions?

A

Occluding junctions
Anchoring junctions
Communicating junctions

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17
Q

Outline occluding junctions

A
  • Links cells to form impermeable barrier
  • In secretory or absorpatory tissue
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18
Q

Outline the scaffolding of tissues

A
  • Most tissues have scaffolding of extracellular fibres set in a jelly like matrix
  • Governs functional organisation of the tissue and dictates the shape of organs
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19
Q

Outline the main fibres of the extracellular scaffolding of tissues

A
  • Main fibres collagen and elastin
    Used because of:
  • High molecular weight
  • Strongly hydrophilic and negatively charged polysaccharide polymers
    -> Retain water to help with turgor pressure
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20
Q

What are glycosaminoglycans?

A

Jelly like complexes

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21
Q

What synthesises glycosaminoglycans?

A

Can be synthesised by many different cells incl. epithelial, muscle, cartilage and bone
But mainly by fibroblasts which can synthesise many different extracellular constituents depending on the environment and mode of stimulation

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22
Q

What can undifferentiated mesenchymal cells become?

A

Osteoblasts (bone)
Chondroblast (cartilage)
Fibroblast (connective tissue)

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23
Q

Outline soft connective tissue

A

Flexible and gel-like
Present in most tissues between major tissue elements
Divisible into fibrous or fatty connective tissue

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24
Q

Outline hard connective tissue

A

Various forms of cartilage and bone

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25
Outline fibrous connective tissue
Contains a large number of fibres e.g collagen, elastin or reticulin Described as loose irregular if few visible fibres that are random or dense irregular if lots of fibres but random Dense regular contains lots of fibres arranged in long parallel bundles
26
Outline fatty connective tissue
Contains mainly fat cells with intervening blood vessels particularly capillaries
27
Outline differentiation between types of collagen
With conventional stained histology you can tell if there are differences in length and thickness but precise composition can't be determined At least 12 types of collagen- biochemical compositions are different But all collagen fibres are not elastic or contractile
28
What does type I collagen do?
Type I- Skin, Bones, teeth, capsules of organs
29
What does type II collagen do?
Cartilage
30
What does type III collagen do?
Liver, kidney, spleen arteries, uterus
31
What does type IV collagen do?
Type IV- Basement membranes
32
What does type V collagen do?
Placenta
33
Outline the structure of collagen
Individual collagen fibrils are made up of overlapping linear strands of tropocollagen (gives rise to characteristic bonding of collagen) Fibrils are aligned side to side to create larger collagen fibres of variable thickness
34
Outline the tropocollagen subunits
Made up of 3 linear polypeptide chains (2 similar and 1 not) Wound together in an alpha helix
35
Outline the connective tissues of the penis
Loose to dense irregular 3 erectile compartments surrounded by a capsule of dense irregular connective tissue surrounding and a tissue with fewer fibres between nerves, blood vessels + lymphatic vessels are also components of connective tissues
36
Outline the structure of elastic tissue
Consists of microfibres of fibrillin and an amorphous matrix of elastin Forms fine fibres or flat sheets
37
Where is elastic tissue found?
Present in most connective tissues and in walls of blood vessels
38
Outline the staining of elastic tissue
Elastin fibres stain pink with H+E stain Sometimes hard to distinguish from collagen but may stain more strongly than collagen and sometimes produce a glassy and refracting light appearance
39
Outline adipose tissue
Some connective tissues contain it 2 types- white and brown
40
Outline white adipose tissue
Most abundant Large cells each with a single fat droplet Protect vital organs and serve as energy stores Fat is deposited alongside capillaries and so usually displays a rich network of fine blood vessels
41
Outline brown fat
Brown fat is abundant in newborns but less so in later life Described as multi-locular as cells contains numerous droplets of fat rather than a single one
42
How is cartilage related to bone?
Along with bone is rigid Closely related to it Bone is ossified cartilage
43
Outline the formation of cartilage
Initially formed by chondroblasts- get trapped in a dense glycosamino rich matrix Matures into chondrocytes Surrounded by fibrous capsule of collagen and perichondrium Contains undifferentiated progenitor- capable of differentiating into chondroblasts if needed Variable amounts of collagen and elastic tissue
44
What are the 3 types of cartilage?
Hyaline Elastic Fibrous
45
Outline the makeup of hyaline cartilage
Has fine fibrils of collagen and elastic (Can't see elastic on light microscope but have glossy appearance on matrix)
46
Hyaline cartilage with staining
Stains poorly with H+E stain
47
Where do you find hyaline cartilage?
Articular surfaces e.g cartilage in trachea All bones are formed from hyaline cartilage which is replaced by bone in a process called endochondral ossification
48
Outline the structure of the elastic cartilage
Fibres a re irregularly arranged and can be seen in the matrix, contains chondrocytes and lots of elastic fibres
49
Where can you find elastic cartilage?
Epiglottis and pinna of ear
50
Outline fibrous cartilage make up
Matrix of cartilage fibrils filled with collagen in bands
51
What is made up of fibrous cartilage?
Intervertebral discs
52
What are the 3 types of muscles and where do you find it?
Smooth muscle- many internal organs and blood vessels Cardiac muscle- heart Skeletal- mainly attached to bony skeleton + is responsible for its stability and movement
53
Outline other cells with contractile properties
Pericytes- along small blood vessels Myofibroblasts- involved in scar formation Myoepithelial cells- assist in expression of milk during lactation
54
Outline the structure of smooth muscle
Discrete cells coupled together by cell junctions They appear fusiform with cylindrical nuclei when cut longitudinally (and round when transversely) Contractile proteins in it are not arranged regularly in repeating sarcomeres (anchored focally in clumps to cell membrane
55
Key features of smooth muscle cells that help it to function
Secrete reticulin external lamina (basement membrane) Joined by gap junctions which permit the stimulus to pass rapidly through the muscle Also have surface receptors to respond to hormonal stimuli
56
Outline gap junctions
Joins 2 smooth muscle cells together Vital for coordinated contraction of smooth muscle The guarded central pole allows small signal molecules to pass from one cell to the next in the chain It electrically couples them and means the signal doesn't need to be transported across the membranes
57
What is the gap junction?
Each one consists of 6 connection proteins that span the cell membranes Forming a central pole
58
Layers of blood vessels from inner to outer
Endothelium Basement membrane Intima Internal elastic lamina Media External elastic lamina Adventitia
59
Outline elastic arteries
Near the heart- aorta and pulmonary Media contains abundant concentric sheets of elastin (seen as red lines)
60
Outline muscular arteries
Most abundant Media made up of layers of smooth muscle with little elastin E.g radial artery, splenic artery
61
Outline arterioles
Resistance vessels Have 3 or fewer layers or fewer muscle layers in their media Up to 100 um diameter Elastic laminae poorly defined
62
Outline structure of capillaries
Only have lumen, endothelium and basement membrane Pericytes on outside to regulate size-> discontinuous layer on outside of small ones which become continuous as they get larger No surrounding muscles or connective tissue
63
Outline fenestrated capillaries
Most tissues have closed capillaries but some have leaky/ fenestrated ones e.g kidney + liver Have holes in endothelium for movement into and out of surrounding tissues
64
Outline veins
No external elastic lamina Thinner walls and larger lumen- media is thinner (than arteries) although large veins thicker compared to venules Smooth muscle in wall might be circular or longitudinal
65
Outline venules
Associated with arterioles Thin walled Contractile pericytes wrap around the outside of endothelial cells and form a complete layer as venules get larger Pericytes replaced by smooth muscle as venules become veins
66
Outline lymphatics
Thin walled similar to capillaries and veins Have valves No blood Contains eosinophilic lymph and maybe lymphocytes (those are mostly in blood tho)
67
nerves
68
Outline plasma
It is blood without the cells Made of water, salt + minerals, plasma proteins (albumin globulins and fibrinogen), hormones, signal molecules, other clotting factors ect.
69
What is serum?
Plasma without clotting factors
70
Outline erythrocytes
Enucleate biconcave discs 6.5-8.5 um in diameter (slightly larger than the smallest capillaries) Live for 4 months Main protein is haemoglobin Cell membrane has an important endoskeleton attached (in which the main protein is spectin)
71
Where are erythrocytes produced and destroyed?
Produced in the liver (foetus) and bone marrow Destroyed in the liver and the spleen producing bilirubin
72
What are the different types of leukocytes?
Granulocytes: Neutrophils (40-75%), Eosinophils (5%), Basophils (0.5%) Agranulocytes: Lymphocytes (20-50%), Monocytes (1-5%)
73
Outline neutrophils
Commonest wbc and granulocyte Multi lobed nucleus, granular cytoplasm, 12-14 um in diameter Circulate in the blood and invade tissue spaces Contain myeloperoxidase- for respiratory burst
74
outline the phagocytic nature of neutrophils
engulf and destroy bacteria and other foreign macromolecules via respiratory burst
75
What are the 3 types of cytoplasmic granule?
Primary granules Secondary granules Tertiary granules
76
Outline primary granules
Lysosomes (myeloperoxidases + acid hydrolases)
77
Outline secondary granules
Specific granules (secrete substances that mobilise inflammatory mediators
78
Outline tertiary granules
Gelatinases and adhesion molecules
79
Outline Eosinophils
1% of total number of wbcs 12-17 um in diameter Bi-lobed nucleus Distinctive large red cytoplasmic granules with crystalline inclusions Have receptors for IgE
80
Outline granules in eosinophils
Large and red with crystalline cores lozenge shaped granules
81
What do eosinophils do?
Numbers increase in parasitic infections or allergic conditions Antagonistic action to basophils- play a role in phagocytosis and to mast cells as they inhibit their secretion Phagocytic with a particular affinity for antigen/antibody complexes Neutralise histamine- restricting inflammatory response
82
Outline basophils
0.5% of white cell series 14-16 um in diameter Bi-lobed nucleus + prominent dark blue-stained cytoplasmic granules Granules contain histamine Have receptors for IgE Circulating form of the tissue mast cell
83
What do basophils do?
Involved in inflammatory regulations and act to prevent coagulation and agglutination Release histamine and vaso-active agents in response to allergens -> results in immediate hypersensitivity reaction - Aka anaphylaxis
84
Outline lymphocytes
Most common agranulocytes 2 main sub types- B Cells T Cells Very few cytoplasmic inclusions so clear blue/grey cytoplasm All subtypes look the same in histological sections on H+E - have to use histochemistry Only blood cell capable of cell division
85
Outline B cells
Become plasma cells and secrete antibodies Called B cells bc they mature in bone marrow
86
Outline T Cells
Are involved in cell mediated immunity Called that because they mature in the thymus
87
Outline T Helper (TH) cells
Help B cells and activate macrophages
88
Outline T cytotoxic (TC) cells
Kill previously marked target cells
89
Outline T Suppressor (TS) cells
Suppress the TH cells so suppress the immune response
90
Natural killer (NK) cells
Mainly kill virus infected cells
91
Outline monocytes
Characteristic reniform nucleus (bean shaped) Although an agranulocyte- it has small cytoplasmic granules (mostly lysosomes)
92
What do monocytes do?
Immature cells circulate briefly in the blood Differentiate into several different cell types within tissue Major phagocytic and defensive role Some cells become APCs, passing antigen fragments to lymphocytes
93
What do monocytes differentiate into?
Tissue macrophages (anywhere) Kupffer cells (liver) Osteoclasts (bone) APCs (everywhere) Alveolar macrophages (lung)
94
Outline platelets
Fragments of cells derived from large multi-nucleated megakaryocytes in bone marrow 1-3 um in diameter Surrounded by cell membrane Contains vesicles with coagulation factors Responsible for clotting of blood notably when endothelium lining blood vessels is breached
95
Outline haematopoiesis
All blood cells form in the haematopoietic bone marrow in adults And liver in foetus
96
Outline myelon series
Lies next to bone and gives rise to white blood cells
97
Outline erythron series
Lies in between trabeculae and gives rise to erythrocytes
98
Outline megakaryocytes
Lie in between bony trabeculae and gives rise to platelets
99
Outline erythropoiesis
Reducing cell size -> haemoglobin production increases -> reduction + loss of organelles -> basophillian early precursors changes to eosinophillian late precursors -> loss of nucleus -> mediated by erythropoeitin
100
Outline Granulopoiesis
Morphologically similar for neutrophils, eosinophils + basophils Increasing number of granules Increasing complex shape of the nucleus
101
Outline the storage of wbcs
Large pool of stored mature neutrophils in marrow No storage of monocytes and lymphocytes complete their precursor maturation either in the thymus or the lymph nodes
102
Outline pericardium
Outermost layer of the heart Has a layer of squamous mesothelial cells resting on thin layer of connective tissue Visceral (outer surface of the heart) Parietal (inner surface of fibrous sack containing the heart)
103
Outline the epicardium
Sometimes used interchangeably with pericardium Strictly it is adipose connective tissue, vessels and nerves Between pericardium and myocardium
104
Outline the myocardium
Thickest layer of the heart Specialised cardiac muscle Endomysium Largest myocytes in wall of left ventricle- smallest in atria Contain perinuclear endocrine granules (atrial naturetic peptide) The heart is an endocrine organ
105
What is a key difference between the action of atrial myocytes and ventricular myocytes?
Atrial myocytes secrete hormones but ventricular myocytes don't
106
Outline the cardiac muscle
Striated, central nuclei (only 1), branching, intercalated discs (only found in myocardium)
107
What is endomysium?
Loose fibrous connective tissue between muscle fibres
108
What are intercalated discs?
Connect adjacent myocytes Contain: gap junctions, adhering junctions, desmosomes
109
Outline the parts of the conducting system of the heart
Sinoatrial node, atrioventricular node, bundle of His, purkinje fibres- specialised myocytes Stains with periodic acid shift- highlights glycogen rich cells Subendocardial, large vacuolated muscle cells
110
Outline the endocardium
Innermost layer of the heart Thin layer of fibrous connective tissue Endothelial cells on innermost layer
111
Outline valves
Covered by endothelium Attached to central fibrous body Fibrosa (dense fibrous CT) Spongiosa (loose fibrous CT) Ventricularis (collagen + elastin)
112
Outline skeletal muscle
Striations - yes Nuclei - multinucleated and on the edge Branching - no
113
Outline cardiac muscle
Striations - yes Nuclei - uni-nucleated and centred Branching - yes (via intercalated discs)
114
Outline smooth muscle
Striations - No Nuclei - Uni-nucleated Branching - No
115
Outline respiratory epithelium
Lines tubular portion of the respiratory system Pseudostratified- all cells connected to the basement membrane Ciliated epithelial cells interspersed with goblet cells
116
What is the purpose of the nose?
Filtration Humidification Warming Olfaction
117
What is the nose lined with?
Made of keratinising and non-keratinising squamous epithelium and respiratory epithelium
118
Key tissue that makes up the nose
Richly vascular lamina propria containing seromucinous glands
119
Borders of the olfactory area
Roof of nasal cavity extending down the septum and lateral wall
120
What is the olfactory area lined with and what glands does it have?
Pseudostratified columnar epithelium of olfactory receptor cells with supporting sustentacular cells and basal cells Glands- serous glands of bowman
121
Outline the nasopharynx functions and epithelial lining
Functions- gas transport, humidification, warming, olfaction Lined by respiratory epithelium
122
Outline the nasal sinuses function and epithelial lining
Functions- lower the weight of the skull, add resonance to the voice, humidify and warm inspired air Lined by respiratory epithelium
123
Outline the larynx function and what it is made up of
Cartilaginous box (hyaline cartilage) Function- voice production Made of - respiratory epithelium, loose fibrocollagenous stroma with seromucinous glands lymphatics and blood vessels common
124
Outline the function of and what vocal cords are made from
Function- voice production Made of - stratified squamous epithelium overlying loose irregular fibrous tissue Also no lymphatics but has blood vessels
125
Outline reinke's space
A potential space between the vocal ligament and the overlying mucosa.
126
Outline the trachea function and what it is made of
Function- conducts air to and from the lungs Made of- respiratory epithelium, seromucinous glands in the submucosa Trachealis muscle posteriorly, c-shaped cartilagenous rings Gap filled by vertically orientated smooth muscle called treachealus
127
Layers of the bronchi
Smooth muscle Partial cartilagenous rings Respiratory epithelium Some basal neuroendocrine cells Seromucinous glands and goblet cells
128
What are the layers of bronchioles?
Smooth muscle Ciliated columnar epithelium Some basal neuroendocrine cells Few goblet cells and clara cells
129
Outline Clara cells make up and location
Most numerous in terminal bronchioles Contain mitochondria, smooth ER, secretory granules Don't contain cilia and have vesicular cytoplasm
130
What do we think that clara cells do?
Secrete a lipoprotein that helps to prevent luminal collapse during exhalation and keeps from sticking together Might play a role in oxidising inhaled toxins, antiprotease function, surfactant production/elimination, stem cells
131
Outline the function and make up of respiratory bronchioles
First part of the distal respiratory tract Function- gas exchange as well as transport, they link terminal bronchioles and alveolar ducts Made up of- cuboidal ciliated epithelium and spirally arranged smooth muscle but no cartilage
132
Size and number of alveoli
150-400 million/lung 250 um in diameter
133
Function of alveoli
Gas exchange
134
Cell types in alveoli
Type 1 pneumocytes Type 2 pneumocytes Alveolar macrophages
135
Outline type 1 pneumocytes
40% of cell population but 90% of surface area Made up of flattened cells, flattened nucleus + few organelles
136
Type 2 pneumocytes
60% of cell population + 5-10% of surface area Made up of rounded cells, round nucleus, rich in mitochondria, smooth and rough ER, spherical bodies Produce surfactant
137
Outline alveolar macrophages
Luminal cells also present in the interstitium, phagocytose particulates including dusts and bacteria-> then either lymphatics or leave via mucocilary escalator
138
Outline the blood air barrier
Made of type 1 pneumocytes- fused basement membrane of pneumocyte and capillary vascular endothelial cells 200-800 nm thick
139
Outline the interstitium
Where endothelial cells are not in direct contact with pneumocytes Made of collagen and elastin fibres, fibroblasts, macrophages Contains pores of Khon- holes in the wall of alveoli helping to equalise pressure
140
Outline visceral pleura
Made of- flat mesothelial cells, loose fibrocollagenous connective tissue Layers- irregular external elastic layer, interstitial fibrocollagenous layer, irregular internal elastic layer
141
Outline oral cavity
What does it do -> receive food, chews food, starts digestion Epithelium -> stratified squamous epithelium on top of connective tissue with keratin layer on top Pathology -> oral cancer-> from SE-> squamous cell carcinoma
142
Outline oesophagus
What does it do-> swallows food Epithelium -> squamous epithelium Submucosal glands
143
Outline stomach
What does it do-> digests food Made up of gastric fundic mucosa => mucus, gastric body mucosa, parietal cells => hydrochloric acid, chief cells => pepsinogen and lipase, gastric antral mucosa Pathology- sometimes contains helicobacter pylori - causes inflammation
144
Intestines function and features to maximise this
What does it do-> digests food, absorbs food, absorbs water, resist bugs Arranged in crypts and villi for larger surface area
145
Layers of the intestines
Epithelium -> Mucosa glandular epithelium all the way down, contains endocrine cells affects timing movement submucosa (all connective tissue) Muscularis propria
146
Crypts- what are they and what do they do
Are moat-like invaginations of the epithelium around the villi. Are lined largely with younger epithelial cells involved primarily in secretion. Contain stem cells at their base, which continually divide and provide the source of all the epithelial cells in the crypts and on the villi. Extend down to the muscularis mucosae.
147
Outline the muscularis propria
2 layers, all smooth muscle, contains ganglion cells Interstitial cells of kahal (pacemaker cells)- can cause tumours called GIST
148
Outline the serosal surface
Outside of the transverse colon Contains- blood vessels, mesentry, mesothelium
149
Parts of the small intestine and what are they covered in
Duodenum, jejunum, ileum Have villi on the folds and microvilli on them contains mucosa associated lymphoid tissue
150
Outline the function of the duodenum
Digests food, absorbs food and resists bugs, bile and digestive enzymes come into it
151
Outline the functions of the jejunum and ileum
Digests food, absorbs food and resists bugs
152
Some diseases of the small intestine
Giardia lambila- parasites on the mucosa Coeliac disease- villi lost and crypt hypoplasia lots of lymphocytes, response to gluten
153
Outline the appendix
What does it do -> Safehouse for the bugs in the gut in case they are all cleared out in response to infection Epithelium -> flat mucosa bc less absorption
154
Outline the colon
Parts of it -> Ascending, transverse, descending, sigmoid What does it do -> absorbs (some) food and water + kills bugs Features-> Villi + folds in the colon Pathology -> ulcerative colitis (inflammation of the mucosa)
155
What are the layers of the muscularis of the stomach?
Innermost oblique layer Middle circular layer Outermost longitudinal layer
156
What is in the portal tract?
Portal veins Arteries Bile ducts
157
Describe make up of the liver
Made up of hepatocytes arranged in cords with intervening sinusoids Liver is divided into lobules
158
Outline the 'classic lobule'
Area drained by one central hepatic venule artificial construct so we can understand hepatic architecture Roughly hexagonal Some hepatocytes will be more richly oxygenated than others
159
Outline the acini of the liver
An architectural concept based around the blood supply rather than the drainage An artificial construct for understanding hepatic architecture
160
Outline hepatocytes
Principle functional cells of the liver Polyhedral epithelial cells
161
What are the 3 important surfaces of hepatocytes?
Sinusoidal (70%)- permits exchange of material with blood (space of Disse) Canalicular (15%)- permits the excretion of bile Intercellular (15%)
162
What do hepatocytes contain?
-Abundant mitochondria (looks like granules) -Large central spherical nuclei -Prominent nucleoli -Might be binucleate -Active golgi apparatus -Prominent endoplasmic reticulum -Numerous peroxisomes
163
Outline sinusoids
Highly specialised blood vessels Thin, discontinuous fenestrated endothelium No basement membrane Contains scattered Kupffer cells
164
Outline the inter-hepatic biliary tree
Epithelium- Simple to cuboidal to columnar epithelium Small: canaliculi -> Bile ductules -> trabecular ducts -> bile ducts :Large
165
Outline canaliculi
Lie between hepatocytes Can't be seen on light microscopy
166
Outline the gallbladder
Functions- concentrates and stores bile, expels bile via common bile duct into duodenum No muscularis mucosa but does contain specialised mucosa and smooth muscle layer
167
Outline specialised mucosa in the gallbladder
Simple columnar epithelium with microvilli Thrown into folds, adapted for water and salt absorption Contains connective tissue - lamina propria
168
Outline the exocrine pancreas
Functions -> To synthesise + secrete enzymes + bicarbonate-rich fluid into the duodenum Has a poorly defined fibrous capsule with septa dividing gland into lobules Epithelial cells arranges in acini
169
Outline acinar cells
Epithelial cells, pyramidal shape Basally - rich in RER Apically - zymogen granules (enzyme precursors)
170
Outline ducts of the liver
Centro acinar cells (fuse to form each other), intercalated ducts, interlobular ducts, main pancreatic duct
171
What are the 3 areas of the kidney?
Cortex Medulla Pelvis
172
What is in the renal cortex?
Glomeruli PCTs DCTs
173
What is a medullary ray?
A collection of loops of Henle and collecting ducts that are in the cortex It occurs when then nephrons have their glomeruli close to the renal capsule
174
Outline the contents of the renal medulla
Comprised of loops of Henle and collecting ducts as well as blood vessels orientated radially from the cortex to the medulla
175
Outline the glomerulus
Tuft of convoluted fenestrated capillaries Glomerular basement membrane Lined by podocytes Supported by mesangial cells Encased in Bowman's capsule Most cells are either glomerular endothelial cells or mesangial cells
176
Outline the glomerular endothelial cells
Nuclei on the inside of capillaries Endothelial cells line the capillaries
177
Outline mesangial cells
Nuclei lie between capillaries Comprise smooth muscle and structural support for the kidney Contraction of it tightens capillaries + reduces glomerular filtration rate Important part of tubular glomerular feedback caused by chemical changes in the glomerulus
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What are the 3 layers of cells of the glomerulus?
Glomerular capillary wall Basement membrane Foot processes of podocytes
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Outline the endothelial cells of the glomerular basement membrane
Inner layer Fenestrated Not so much that it lets big molecules like albumin
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Outline the basement membrane of the bowman's capsule
Double thickness Fusion of bms, podocytes and epithelial basement membrane Has a lamina lucida, double thickness lamina densa and a lamina externa Contains collagen and -ively charged heparin sulphate molecules So -ive ions in plasma experience repulsive force
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Outline podocytes in the glomerular basement membrane
Have foot process that interdigitate Made up of several proteins Leaves a small space bridged by a -ively charged membrane
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Outline juxtaglomerular apparatus
2 components- afferent arteriole, distal convoluted tubule Afferent arteriole contributes granular cells Secrete renin in response to low BP DCT has macula densa cells
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Outline macula densa cells
Patch of closely packed endothelial cells along the tubule Senses NaCl conc. and regulates tuboglomerular feedback
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Outline lacis cells
In juxtoglomerular apparatus Don't know what they do
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Outline the lining of the proximal convoluted tubule
Lined by cuboidal epithelium Round central/ basal nuclei Brush border of microvilli on apical end Many mitochondria so appears eosinophillic
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What is the function of the PCT and where is it?
Reabsorption of NaCl, proteins, polypeptides, amino acids, glucose In renal cortex
187
Outline the loop of Henle
Descending and ascending limbs Both with thick and thin segments supplied by rich vasa recta in between the loop
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Epithelial lining of the loop of Henle
Simple squamous epithelium
189
Outline the epithelial lining of the DCT
Simple cuboidal epithelium Numerous mitochondria Shorter than PCT
190
What does the DCT do?
Regulates acid base by secreting H+ and absorbing HCO3- (via cellular carbonic anhydrase) Regulates Na+ level by exchanging Na+ for K+
191
Outline the collecting duct
Principal cells respond to aldosterone and ADH Intercalated cells exchange H+ for HCO3- 3 types: cortical, medullary and papillary ducts
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What are the 3 types of collecting ducts lined with?
Cortical collecting ducts - simple cuboidal epithelium Medullary collecting ducts - simple columnar epithelium Papillary ducts - simple columnar epithelium
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Progression of the kidney blood supply (from source to nephron)
Abd aorta -> Renal artery at L1 -> Anterior + posterior division -> Interlobar artery -> Arcuate artery (corticomedullary) -> Interlobular artery -> Afferent arteriole
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Progression of the blood supply to the loop of Henle
Efferent arteriole (from renal corpuscle) -> Peritubular arteries -> Vasa recta -> Renal veins -> Inferior vena cava
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Outline the renal pelvis
Collecting ducts drain into it Lined by urothelium - multi-layered stratified Transmits filtrate from nephron to ureter
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Outline urothelium
Specialised epithelium found in the collection/ drainage parts of the urinary tract Complex stratified epithelium
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What are the layers of the urothelium
Layer of large dome shaped umbrella cells overlies a pseudostratified layer of polygonal cells Intermediate layer Basal layer- cuboidal cells can stretch
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Outline ureters
Lined by urothelium (transition epithelium) Spiral muscular tube Inner 'longitudinal' Outer 'circular' (different to GI arrangement) No serosa Loose adventitis
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Outline the layers of the urinary bladder
Layers- urothelium, lamina propria, muscularis mucosa (poorly developed), submucosa, muscularis propria(well developed), subserosa, serosa Functional valve prevents reflux into ureter bc of passage of ureters thru muscularis propria
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Outline the female urethra
4-5cm long Lined by -> Proximally: transitional epithelium; Distally: squamous epithelium Paraurethral and periurethral glands open into urethra
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Outline the male urethra
20cm long Parts- 1. Prostatic urethra 2. Membranous urethra- lined by urothelium 3. Penile urethra- lined by pseudostratified epithelium proximally, stratified squamous epithelium distally
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Outline the testis
Paired organ in the scrotum Average weight 15-19g
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What are the 3 layers of the capsule of the testis (outer to inner)?
Tunica vaginalis- Tunica albuginea Tunica vasculosa
204
Outline the tunica vaginalis
Projection of the peritoneum Flattened layer of mesothelial cells on a basement membrane)
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Outline the tunica albuginea
Collagen fibres with some fibroblasts, myocytes and nerve fibres
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Outline the tunica vasculosa
Loose connective tissue containing blood vessels and lymphatics
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Pathway of spermatozoa out of the testes
Seminiferous tubules -> Straight tubules -> Rete testis -> Efferent ductules in the head of the epididymis -> Epididymis -> vas deferens -> Ejaculatory duct -> Membranous urethra -> Penile urethra
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Describe testicular parenchyma lobules
Divided into lobules by septa originating from the capsule Around 250 lobules Each lobule contains 1-4 seminiferous tubules
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What cells are in seminiferous tubules?
Germ cells in various stages of maturation Sertoli cells
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Progression of sperm maturation from spermatozoon to type A spermatogonia
Spermatozoon -> Spermatid -> secondary spermatocyte -> Primary spermatocyte -> Type B spermatogonia -> Type A spermatogonia
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What are type B spermatogonia?
Differentiating progenitor cell Has spherical nuclei with densely stained masses of chromatin
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What are the two versions of type A spermatogonia?
Darkly stained (Ad) Pale stained (Ap)
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Outline sertoli cells
Columnar cells on the basement membrane of the tubule Send cytoplasmic projections around the sperm cells Nuclei are irregularly shaped, folded and have prominent nucleolus Cytoplasm is eosinophilic and may contain lipid granules
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What do sertoli cells do?
Supportive, phagocytic and secretory functions
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What are the different parts of spermatozoa?
Head Neck Midpiece Principle piece End piece
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What is included in the head of the spermatozoa?
Acrosomal cap and nucleus
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What is included in the midpiece of the nucleus?
Spiral mitochondria around the axomere
218
What is in the neck and tail of spermatozoa?
Axomere and plasma membrane
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What does the axomere do?
Responsible for cell motility Basically long cillia
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Outline leydig cells
Present singly and in clusters in the interstitium between tubules Abundant cytoplasm containing lipid Contain peinke's crystalloids- eosinophilic crystalloids (not seen before puberty) Produces testosterone
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Outline the rete testis
Anastomosing network of tubules at the hilum of the testis Receive luminal contents from seminiferous tubules Lined by simple squamous or low columnar epithelium on a relatively thick basement membrane Have cilia at luminal surface
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Function of the rete testis
Mixing chamber for contents of the seminiferous tubules Possible secretions Reabsorption of protein from luminal contents
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Outline the efferent duct
12-15 convoluted tubules which empty into the epididymis Lined by ciliated and non ciliated simple columnar epithelium with interspersed cuboidal cells (basal cells) giving pseudostratified appearance
224
Outline the epididymis
A tubular structure 4-5cm long containing highly convoluted epididymal duct Lined by tall columnar cells with long atypical cilia Epithelium is supported by a thick basement membrane surrounding which is a well defined muscular coat
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What does the epididymis do?
Site of absorption of testicular fluid Phagocytosis pf degenerous spermatozoa Produces secretion rich in glycoproteins, amino acid and glycerophosphyl choline Play a role in maturation of the spermatozoa
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Outline the vas deferens
30-40cm tubular structure arising from the caudal portion of the epididymis Distal part enlarged to form the ampulla which joins the excretory duct of the secretory vesicle to form the ejaculatory duct Lined by pseudostratified columnar epithelium comprising columnar and basal cells Has a thick muscular wall of 3 layers
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Shape, weight and position of the prostate
Pear shaped glandular organ Weighs up to 20g in young adults (enlarges with age) Surrounds the bladder neck and prostatic urethra
228
What are the lobes of the prostate gland?
Anterior Middle Posterior 2 lateral lobes
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What are the gland regions of the prostate?
Peripheral- (most common site of cancer) Central Transitional Periurethral
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Key parts of the prostate gland
Covered by ill defined fibroconnective tissue capsule Glandular and non-glandular components Ducts- large primary and small secondary Acini- 30-50 tubuloalveolar glands with convoluted edges
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What are acini of the prostate lined by?
Lined by secretory cells, basal cells and neuroendocrine cells Cells rest on a basement membrane
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What do secretory cells do and where are they in the acini?
Located in the luminal side of the glands Secrete PSA and PAP into the seminal fluid Helps to liquify the semen
233
What do the basal cells of acini form?
A continuous layer
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What is stroma made up of?
Smooth muscle Fibroelastic fibres Blood vessels Nerves
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What happens to stroma and glands of prostate with increasing age?
Undergo hypoplasia
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Outline seminal vesicles
Paired, highly coiled tubular structures posterolateral to the bladder The duct empties into the ejaculatory duct Lined by tall, non-ciliated columnar epithelium Vacuoles and lipofuscin Secretions act as nutrients for spermatozoa
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What are the layers of the seminal vesicles?
Mucosa (folded) Smooth muscle (2 layers) Adventitia
238
Outline the 3 components of the erectile tissue
Left and right corpora cavernosa on the dorsal side (lined by vascular endothelial cells) Corpus spongiosum on the inferior side
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Outline the make up of erectile tissue of the penis
Comprises irregular vascular spaces separated by fibroeslastic tissue and smooth muscle Has a rich nerve supply
240
Outline the ovary
Paired organ either side of the uterus close to the pelvis wall
241
What are the attachments of the ovaries?
To broad ligament by mesovarium To uterus by utero ovarian ligament To pelvic wall by suspensory ligament
242
What is the ovary made up of?
Covered by a single layer of modified mesothelium A poorly defined connective layer called tunica albuginea Stroma
243
Outline the stroma of the ovary
Divided into the cortex and medulla with indistinct boundaries
244
What is the hilum of the ovary?
Point blood vessels and lymphatics enter
245
What is the ovarian cortex?
Spindle stromal cells arranged in whorls/storiform pattern
246
What do ovarian follicles contain?
Some leutinised cells
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What is in the ovarian medulla?
Loose fibrous elastic tissue with blood vessels, lymphatic and nerves
248
Outline the rete ovary
Similar to the rete testis, present at hilum of ovary
249
Outline primordial follicles
Located in periphery of the cortex Contains primary oocyte in a resting state Surrounded by a single layer of epithelial cells (granulosa cells) 30-40 develop at once
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Primary follicles- how are they formed
1. Cyclic FSH secretion from ant. pit. 2. Stimulates follicular development 3. Follicular epithelial cells proliferate 4. Oocyte enlarges 5. Stromal cells organise to form a connective tissue sheath 6. Zona pellucida forms around oocyte
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What does the epithelium of the stroma change from and to?
Squamous to cuboidal/columnar
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Glycoproteins between granulosa cells and oocyte
253
What is the antrum?
Space filled with follicular fluid
254
Describe the formation of secondary follicles
Formation of the antrum Theca differentiates into inner theca interna and outer theca externa Oocyte is supported in antrum by a stalk of granulosa cells (clumbus oophorus)
255
Outline the mature (graafian) follicles
Ovum surrounded by thick zona pellucida, corona radiata, basal lamina, theca interna and externa Has a cumulus oophorus which suspends the ovum in the grafian follicle
256
Corpus luteum
Forms from follicle Via luteinisation of granulosa cells and theca cells (stimulated by LH) These cells become polygonal and have lots of cytoplasm containing lipid Secretes progesterone and oestrogen
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What is the corona radiata?
Layer of granulosa cells that surrounds the oocyte
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Numbers of eggs made and released in ovaries
Approx 1 mill at birth but only 400-500 mature At ovulation 1 follicle ruptures out of the ovary (leads to bleeding in antral space)
259
Common features of the endocrine system
- Glandular epithelium apart from post. pituitary gland - Richly vascularised - Secrete a variety of hormones - Controlled by +ve and -ve feedback loops
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Pituitary overview
- Coordinates the endocrine organs through the feedback loops - Two functional components: - Post. pituitary - Ant. pituitary
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Posterior pituitary
- Downward extension of the hypothalamus - Neural tissue: - Axons - Glial cells - Stores/secretes: - Oxytocin - ADH
262
Anterior pituitary
- Nested epithelial pituicytes - Richly vascular fibrous stroma - Several different types of pituicyte not distinguishable on H+E Can be stained with reticulin
263
Anterior pituitary cell make up
Cell % Hormone Somatotrophs 50% Growth hormone Lactotrophs 25% Prolactin Corticotrophs 15-20% ACTH, a-MSH, b-lipotrophin, b-endorphin Gonadotrophs 10% FSH, LH Thyrotrophs 1% TSH
264
Somatotrophs- Ant. pituitary
- Diffuse cytoplasmic GH +ve (stains with it) - Lateral wings of ant. pituitary - Present throughout gland
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Lactotrophs - Ant. pituitary
- Polygonal cells - Cytoplasmic processes wrap around other cells - Variable Prolactin staining- stains cytoplasm brown
266
Thyrotrophs- Anterior pituitary
- Angular chromophobes - Don't stain with H+E -Elongated cytoplasmic processes - Variable TSH staining
267
Gonadotrophs- Anterior pituitary
- Scattered round/oval cells - Stain with either: - Alpha subunit - Beta LH - Beta FSH
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Corticotrophs- Anterior pituitary
- Round basophilic cells - Stain dark purple on H + E - Median of gland - Large cytoplasmic vacuoles ("enigmatic bodies")
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Supporting cells- Anterior pituitary
- Sustentacular cells - Surround the normal follicles - S100 +ve (stains brown with it)
270
Pineal gland
- Located just below the posterior end of the corpus callosum - covered by meninges - Irregular lobules - Pinealocytes in rosettes (neuron-like) - Secretes melatonin- in response to autonomic stimulation - Eosinophillic cytoplasm + round central nuclei - Brain sand- accumulation of calcium
271
Thyroid
- In neck anterior and lateral to the trachea - Combination of follicular cells and colloid - Richly vascular - Produces thyroxine and calcitonin
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Parathyroid glands
- 4 glands, variably located in the neck - Produce parathyroid hormone (PTH)- important in calcium homeostasis - 3 cell types: - Chief cells - Oxyphils - Adipocytes
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Chief cells- parathyroids
- Functional cells of the gland - Polygonal cells - Scant cytoplasm - so tissue appears blue bc of lots of nuclei - Secrete PTH - Raises serum Ca2+ - Bone - Kidney - Gut
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Staining of chief cells (parathyroid)
- Strong immunoreactivity for PTH - No calcium oxalate crystals (unlike thyroid so can be used to determine what the tissue is)
275
Oxyphil cells- parathyroid
- Large polygonal cells - Increase with age - Abundant eosinophilic cytoplasm - Finely granular- rich in mitochondria? - Unknown function
276
Endocrine pancreas
Islets of langerhans
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Islets of Langerhans
- Approx 1 million - Balls of cells - Thin fibrous capsule - Mostly in pancreatic tail
278
Hormones secreted by the islets of Langerhans
Cell % Hormone B (beta) cells 70% Insulin A (alpha) cells 20% Glucagon D (delta) cells 5-10% Somatostatin PP cells 1-2% Pancreatic polypeptide
279
Adrenal cortex
- Back of abdomen (retroperitoneal) on top of kidneys - 2 layers- Cortex and medulla
280
Adrenal cortex
- Zona Glomerulosa - Mineralocorticoids - Zona Fasciculata - Glucocorticoids - Zona Reticularis - Androgneic steroids
281
Zona glomerulosa (outermost layer of the adrenal cortex)
- Secretes aldosterone - Thin, incomplete layer - Small cells - Vacuolated cytoplasm
282
Zona fasciculata (middle layer of the adrenal cortex)
- Secretes cortisol - Most prominent layer - Large polygonal cells - Almost clear cytoplasm (bc of abundance of lipid)
283
Zona reticularis (inner layer of the adrenal cortex)
- Produces androgenic steroids - Anastomosing columns of small polygonal cells
284
Adrenal medulla
- Centre of adrenal gland - Chromaffin cells - Large, polyhedral - S100 +ve (stains with it) - Produces adrenaline and noradrenaline
285
Outline the corpus albicans
Well circumscribed structure with convoluted borders almost entirely composed of densely packed collagen with occasional follicles Eventually they may be resorbed/replaced by ovarian stroma
286
What happens to the corpus luteum if there is no pregnancy?
It regresses as 8-9 days after ovulation granulosa cells change size and develop pyknotic nuclei + accumulate abnormal lipid cells then undergo dissolution and are phagocytosed There is progressive fibrosis by ingrowth of connective tissue
287
What are the 4 segments of the fallopian tube?
Intramural- inside uterine wall Isthmus- 2-3 cm thick walls Ampulla- expanded area Infundibulum- trumpet shaped opening to the peritoneum
288
Outline the fallopian tube
Run thru the length of the broad ligament Transport the ovum to the uterus Fertilisation occurs here
289
Endometrium in menstrual phase
Progesterone stimulation withdrawn Stromal haemorrhage and granulocytes Stromal and granular fragmentation Might see mitotic figures
290
Outline the mucosa of the female reproductive tract
Thrown into branching folds (plicae) 2 Cell types: - Secretory- Most prevalent at uterine end - Ciliated- most prevalent at infundibular end (peg cells and basal cells)
291
Outline the muscularis (myosal pinx)
Inner circular layer- tightly wound spiral Outer longitudinal layer- looser spiral
292
Fallopian serosa
Connective tissue covered by mesothelium
293
Endometrium in menstrual phase
Progesterone stimulation withdrawn stromal haemorrhage and granulocytes Stromal and granular fragmentation Might see mitotic figures
294
3 layers of the uterus
Endometrium Myometrium Serosa
295
Endometrium in secretory phase
Progesterone stimulation Early -> below nuclear glycogen vacuoles Mid -> vacuoles above and below nucleus and intraluminal secretions, glands more rounded, stromal oedema (no H+E staining) Late -> Elongated and saw toothed glands with more intraluminal secretions -> stroma-spiral arterioles and decidual change
296
Outline the endometrium in proliferation phase
Oestrogen stimulation Straight proliferating glands with mitotic activity No luminal secretions Stromal cells are spindled and show mitotic activity
297
What are the 2 layers of the endometrium?
Deep basal layer- stratum basalis- reserve of endometrial cells- replenished Superficial layer- stratum compactum (towards the surface and stratum spongiosum- lost during each menstrual cycle
298
What does it mean for the endometrium to be hormonally responsive?
Its appearance changes depending on the phase of the menstrual phase
299
Outline the myometrium
Thick muscular wall with 3 ill defined layers of smooth muscle: Inner longitudinal Middle circular Outer longitudinal
300
What are the 2 layers of the cervix?
Endocervix Ectocervix
301
Outline the endocervix
Loose fibromuscular stroma lined by simple columnar ciliated epithelium Thrown into crypts- crypts not glands as epithelium is all the same
302
Outline the ectocervix
Dense smooth muscle stroma lined by non-keratinised stratified squamous epithelium Site of squamocolumnar junction varies (most common site for cervical cancer) - might lie at os or ectocervix Atrophic in post menopausal women
303
Mucosa of the vagina
Lined by non-keratinising stratified squamous epithelium Stroma contains elastic fibres and a rich vascular network
304
Key facts about the epithelial lining of the mucosa of the vagina
Accumulates glycogen -> maximal around ovulation It becomes more spongy
305
Outline the muscular wall of the vagina
Smooth muscle cells Inner circular Outer longitudinal
306
Adventitia of the vagina
Loose connective tissue
307
Structures of the vulva
Mons pubis, clitoris, labia minora, labia majora, vulvar vestibula, hymen, urethral meatus, skein's gland, bartholin's gland, introitus
308
Outline the labia majora epithelium
Looks like normal skin Lined by keratinising stratified squamous epithelium and has skin adnexae
309
Outline the labia minora epithelium
Mostly non- keratinising stratified squamous epithelium
310
Outline Bartholin's gland
Tubuloalveolar glands-> acini lined by mucus secreting epithelium
311
Minor vestibular glands
Simple tubular glands lined by mucus- secreting epithelium
312
Skein's glands (periurethral glands)
Analogous to prostate lined by pseudostratified columnar epithelium
313
Outline the lining of the hymen
Lined by non-keratinising squamous epithelium
314
Outline the clitoris
Erectile tissue rich in blood vessels and nerves
315
Contractile cells that are not muscle
Pericytes, myo-fibroblasts, myoepithelial cells
316
Outline skeletal muscle components
Myoblasts fused to form multi-celled syncitium Sarcomeres joined end to end to form myofibrils Cytoplasm filled with myofibrils to form muscle fibre Muscle fibres clump together to form fascicles Held together by connective tissue endomycium, perimycium and epimycium
317
Key facts about skeletal muscle fibres
Multi-nucleated- bc formed from multiple cells Dark stained nuclei (at edges) Pink stained cytoplasm with striations 10cm long and 50-60um wide- elongated fibres Voluntary Non branching
318
What is in a skeletal muscle cell?
Cell membrane- aka sarcolemma Nuclei Contractile proteins Mitochondria Endoplasmic reticulum- sarcoplasmic reticulum Glycogen-rich cytoplasm- sarcoplasm
319
Why is skeletal muscle striated?
Myofibrils are in register So light bands and dark bands of each sarcomere line up
320
Difference between a myocyte, myofibril and sarcomere
Myocyte- whole cell Myofibril- arrangement of contractile proteins in a muscle fibre Sarcomere- functional units of the myofibrils
321
What makes up the sarcomere?
Actin- thin filaments Myosin- thick filaments Accessory proteins
322
How are the proteins arranged in sarcomeres
Actin filaments anchored by accessory proteins that form Z lines (sarcomere is what is between 2 z-lines) Areas where there is only actin (i-bands) and only myosin (a-bands)
323
Different types of skeletal muscle fibre
2 broad types Not distinguishable on H+E Type 1- rich in fibrillar ATPase, slow twitch Type 2- rich in fibrillar ATPase, fast twitch (also split up into fatigue sensitive and fatigue resistant)
324
How do muscle spindles detect stretch and tension?
Fibrocollagenous capsule Intrafusal muscle fibres (wrapped around by gamma efferent nerve fibres) Detect stretch and tension
325
Outline Endomysium
Collagenous connective tissue between muscle fibres
326
Perimysium
Fibrocollagenous connective tissue Binds muscle fibres to form fascicles
327
Epimysium
Connective tissue that binds all of the fascicles together around the outside
328
Sharpey's fibres
Connect muscle to bone (and penetrate bone) Bundles of collagen linking epimysium to periosteum Attach muscle to bone over a wide area e. g rotator cuff muscles attached to scapula
329
Tendons
Connect muscle to bone over a small area Made of parallel bundles of collagen with intervening fibroblasts e.g rotator cuff muscles attached to humerus
330
What are the cells that make up bone?
Osteoprogenitor cells Osteoblasts Osteocytes Osteoclasts
331
What is in the extracellular matrix?
Collagen and calcium hydoxyapatite
332
Outline osteoblasts and osteocytes
- Derived from embryonic mesenchyme (osteoprogenitor cells) - Secrete osteoid (unmineralised bone) - Become trapped in their own matrix - Connect to surrounding cells via canaliculi (where oxygen and nutrients diffuse)
333
Difference between osteoblasts and osteocytes
Osteocytes are osteoblasts that have moved from the outer layer of the bone into the matrix and have been trapped there
334
Outline osteoclasts
- Derived from monocytes - Large, multinucleate cells - Absorb bone- sit in Howship's lacunae- depressions in the bone - Activity is linked to osteoblasts (via rank ligand)
335
What are the ways we can differentiate types of bone?
By origin By gross appearance (2 ways) By mode of formation
336
What are the two categories of bone differentiation by origin?
Primary (woven) Secondary (lamellar)
337
What are the 2 categories of bone by gross appearance (1)?
Spongy/cancellous Compact
338
What are the 2 categories of bone by bone formation?
Membranous Endochondrial
339
What are the 2 categories of bone by gross appearance (2)?
Osteons Appositional
340
What is osteoid?
An extracellular matrix rich in type 1 collagen, glycosaminoglycans and proteoglycans
341
How is bone formed?
Osteoblasts lay down osteoid, in which the glycosaminoglycans include osteocalcin which has a strong affinity for calcium ions Osteoid then mineralised when there is a high conc. of calcium and phosphate ions via osteocalcin and alkaline phosphatase Calcium deposited in bone as calcium hydroxyapatite
342
Lamellar bone
Osteoid is deposited in parallel sheets Remodelled from woven bone
343
Woven bone (aka primary bone)
Osteoid is deposited haphazardly and is laid down rapidly in foetal bone and at fracture sites Has a disorganised collagen fibre architecture and is mechanically weak
344
Cement line
Faint blue line (on H+E) Between osteoid and bone
345
Osteocalcin- what does it do?
Binds calcium ions to osteoid
346
Outline secondary/lamellar bone
Stronger - Forms as osteons - Has central Haversian canal containing blood vessel - Surrounding concentric rings of lamellar bone with osteocytes
347
How is secondary bone usually stained and examined?
Typically examined as a decalcified section stained with H+E
348
What bones are formed by intramembranous formation?
Flat bones of the skull Some cortical bone shafts
349
What bones are formed by endochondrial formation?
All other bones- formed from cartilagenous formation
350
Key facts about Intramembranous ossification
Formation of bone from a membranous precursor Occurs in the formation of flat bones of the skull Bone deposited directly in an embryonic mesoderm- without a cartilaginous proforma Begins in second trimester
351
Outline the process of intramembranous ossification
Initially, small clusters of progenitor cells within a primitive mesenchyme transform into osteoblasts and deposit islands of bone These islands coalesce as the enlarge creating an open meshwork of bone and continue to do so until they form a primary plate of bone Woven bone then remodelled to lamellar bone
352
Endochondrial ossification
Converts a hyaline cartilaginous template into bone Cartilaginous proformas form in the second trimester
353
Outline the process of endochondral ossification
Shaft/dyaphisis becomes calcified and blood vessels grow into developing bone Osteoprogenitor cells then differentiate into osteoblasts which lay down bone to form a primary centre of ossification Proforma cartilage is eroded away as new bone forms Later secondary centres of ossification form head/ epiphysis of bones As ossification centres expand, cartilage is restricted to epiphyseal growth plates and articular surface
354
Do bones have centres of ossification at birth
By birth most bones have primary centres of ossification and some have secondary ones
355
What are epiphyseal growth plates
Separate the epiphysis from the diaphysis
356
How is the zone of hyperplasia formed from the resting cartilage?
Chondrocytes in the resting cartilage divide creating columns of new cells - a zone of hyperplasia
357
How is the zone of hypertrophy formed from the zone of hyperplasia?
Cells of zone of hyperplasia enlarge
358
How is the zone of ossification formed from the zone of hypertrophy?
As chondrocytes enlarge they erode the extracellular matrix The remaining strands of matrix become calcified and serve as a substrate for the attachment of osteoblasts
359
Outline synovium
- Lines the inside of the joint capsule - 1-4 layers of synovial cells - Type A- phagocytes - Type B- rich in RER - Variable shapes- squamous to cuboidal - Richly vascular and highly innervated
360