Appunti Anatomia (Anatomy, Anatomical and Physiological Bases of Organ Pathologies)

Anatomy

What are we made of?

• Hydrogen
• Oxygen
• Carbon

Planes and sections

The frontal plane extends from side to side dividing the body into anterior and posterior sections.

The sagittal plane extends from anterior to posterior, dividing the body into left and right sections.

Anatomy

Derived from anà (through) and temmò (cut), anatomy translates to "dissect into parts." It studies the structures by dissection and the relationship between the parts of the body and the structure of single organs.

Anatomy vocabulary: directions

Anterior/Posterior

Superior/Inferior

Medial/Lateral

Proximal/Distal

• Left and right refer to the sides of the subject, NOT the observer.
• Some reference terms are equivalent, e.g., posterior and dorsal, anterior and ventral.
• Medial: approaches towards the medial axis of the body.
• Lateral: moves away from the medial axis of the body.
• Proximal: approaches towards the trunk’s attachment point.
• Distal: moves away from the trunk attachment point.

Body cavities

The human body is not a solid object: many organs are suspended in internal chambers called body cavities:

• Cranial cavity
• Vertebral canal
• Thoracic cavity
• Diaphragm
• Abdominal cavity
• Pelvic cavity

Cardiovascular system

Components and functions

This system is made by: heart, arteries, veins, and capillaries.

The functions of this system include the transport of oxygen and nutrients, and removal of waste products. Other functions are related to thermoregulation, immune system action, and homeostasis.

Heart, the pump

A hollow organ divided into two parts that NEVER communicate – two non-communicating halves (one right and one left). Each half presents two communicating cavities, the atrium and the ventricle (left and right). The heart does NOT stand upright but lays on the diaphragm.

Circuits

• 1 big circuit (systemic circuit): Starts at the left ventricle (aorta artery) and ends at the right atrium (vena cava inferior, superior, and coronary sinus).
• 2 small circuit (pulmonary circuit): Starts at the right ventricle (pulmonary artery) and ends at the left atrium (4 pulmonary veins, 2 from each lung).

In the pulmonary circuit, arteries transport blood low in oxygen, whilst veins transport blood rich in oxygen.

Veins and arteries

Veins: transport blood TOWARDS the heart.

Arteries: transport blood AWAY from the heart.

Heart location

Located between the lungs, with about 2/3 of its mass to the left of the midline. It is located in the thoracic cavity in the anterior mediastinum, lays on the diaphragm, and is protected by the sternum and costal cartilages.

Pericardium

The pericardium is a fibrous sac wrapped around the heart that fixes it to the diaphragm and separates it from the surrounding organs.

• Fibrous pericardium: connective tissue, prevents hyperextension of the heart.
• Serous pericardium: thinner and more delicate, consisting of two membranes (visceral pericardium and parietal pericardium) within which the pericardial fluid flows.

External morphology

The heart is a cone-shaped hollow organ and has the size of a fist, weighing less than 400 grams.

• Apex: directed forward, down, and to the left, rests on the diaphragm at the level of the 5th intercostal space.
• Base: the postero-superior portion, includes the origin of the main vessels and the upper portions of the atria, located at the level of the 3rd costal cartilage.
• Left or obtuse border: belongs to the left ventricle.
• Right or acute border: constituted by the right atrium.
• Anterior or sterno-costal face: mainly right ventricle.
• Diaphragm face: mainly left ventricle.
• Coronary sulcus or atrioventricular sulcus: marks the boundary between atria and ventricles.
• Anterior and posterior interventricular sulcus: marks the boundary between right and left ventricles hosting coronary vessels.

Heart layers

The heart consists of three layers:

• Epicardium: covers the outer surface of the heart, corresponds to the visceral pericardium, thin and transparent.
• Myocardium: myocardial muscle tissue (thickness proportional to the work done).
• Endocardium: simple squamous epithelium (endothelium) that lines the internal surface of the heart covering the inside of the myocardium and continues with the endothelium of the vessels.

Myocardium

Muscular tissue made up of cardiomyocytes (cardiac muscle cells), cylindrical in shape with the ends divided into two or more branches, a central nucleus, and a high number of mitochondria.

They are connected to each other from mechanical, chemical, and electrical points of view, constituting a functional syncytium. The contraction of each cell causes the contraction of several others, thanks to the gap junctions – channels that connect cardiomyocytes to each other.

Fibrous skeleton of the heart

Cardiomyocytes are gathered in bundles of varying sizes that fit on the fibrous skeleton of the heart, a group of robust connective rings that:

• Support the binding of muscle tissue.
• Give support to the heart valves.
• Separate atrial musculature from the ventricular one.

The fibrous skeleton is located in correspondence with the valve plane, at the level of the atrioventricular limit. It's made of dense fibrous connective tissue.

Coronary vessels

They vascularize the heart, using 5% of cardiac output, mainly during diastole. It is a terminal circulation, meaning a region is vascularized only by the vessels deriving from a single arterial branch. In case of occlusion, the territory undergoes necrosis.

• Right coronary artery: right atrium, part of both ventricles, part of the conduction system.
• Left coronary artery: left ventricle, left atrium, interventricular septum.

Venous return – cardiac veins

The great cardiac vein and middle cardiac vein collect blood from the veins that drain the myocardial capillaries and end into the coronary sinus. The coronary sinus is located in the posterior portion of the coronary sulcus and opens into the right atrium, inferior to the inferior vena cava.

The anterior cardiac veins that drain the anterior surface of the right ventricle enter directly into the right atrium.

Internal morphology

Four cardiac cavities: atria and ventricles, separated by the atrial septum and the interventricular septum.

• The two atria are separated by the atrial septum just as the interventricular septum separates the right ventricle from the left one.
• Unidirectionality of the blood flow is maintained through valves.

Atria

The internal surface is smooth in the portion between the outlet of the large veins, while it has a trabecular aspect laterally and anteriorly, with the maximum expression in the auricles. In the atrial floor, there is the atrioventricular orifice equipped with a valve.

Right atrium

• Superior vena cava: blood from head, neck, upper limbs, and chest.
• Inferior vena cava: blood from abdomen, viscera, and lower limbs.
• Coronary sinus: receives blood from the heart veins.

Fossa ovalis: residue of the foramen ovale which in fetal life allows the blood to pass from the right to the left atrium (fetal circulation).

Left atrium

Receives the outlet of the 4 pulmonary veins (2 from the right lung and 2 from the left lung) at the level of the posterior wall.

Ventricles

The internal surface has irregular muscle reliefs, the trabeculae carneae, which make up the papillary muscles. From the papillary muscles, bundles of collagen fibers originate – the tendon cords – which are inserted on the flaps of the atrioventricular valves.

• Each ventricle has an atrioventricular (AV) orifice, which communicates with the corresponding atrium.
• An arterial orifice, which represents the origin of the respective artery, pulmonary on the right, aorta on the left.

Each heart cavity is equipped with a valve, made up of dense connective tissue to prevent the backflow of blood in the wrong direction.

Cardiac valves

The atrioventricular valves are located between the atria and ventricles and are:

• Tricuspid: between RIGHT atrium and ventricle.
• Bicuspid (or mitral): between LEFT atrium and ventricle.

Arterial valves (semilunar valves) consist of three pocket folds that allow the passage of blood from the ventricle to the corresponding artery:

• Pulmonary valve is located at the emergence of the pulmonary trunk from the right ventricle.
• Aortic valve is located at the emergence of the aorta from the left ventricle, at the level of which the right and left coronary arteries originate.

When an AV valve is open, the semilunar valves are closed, and vice-versa. The portion of the ventricular cavity adjacent to the AV orifice is called the inflow portion as it receives blood from the atrium. The portion adjacent to the arterial orifice is called the outflow portion because it pushes the blood into the relative artery.

Right ventricle

Has thin walls as it only pushes blood into the pulmonary circulation and it has 3 papillary muscles.

Left ventricle

This chamber has the thickest walls, as it pushes the blood into the entire systemic circulation. The flesh trabeculae are more prominent and only 2 papillary muscles are present.

Blood flow

Blood flows through the heart from areas of higher pressure to areas of lower pressure, resulting in the opening of the valves and contraction of the subsequent chambers.

• Ventricular diastole (relaxation): blood flows from the ventricles, filling them; AV valves are open; semilunar valves are closed.
• Ventricular systole (contraction): blood flow opens the semilunar valves while the blood flowing back to the atria closes the cusps of the AV valves. The contraction of the papillary muscles and the tension of the tendon cords prevent the overturning of the cusps towards the atrium, preventing blood reflux.

Valvular pathologies

Auscultation is carried out through the use of a stethoscope whose positioning varies depending on the valve to be examined. Generally, it is possible to perceive the first and second tones accompanying the movements of the valves:

• The first tone marks the beginning of ventricular contraction and is produced by the closure of the AV valves.
• The second tone, shorter, corresponds to the ventricular diastole when the semilunar valves close.

Conducting system of the heart

Self-generated: the contraction is autonomous, it arises independently of nerve or hormonal stimuli. Nerve or hormonal stimuli can only change the frequency of the contraction. Each contraction follows a precise sequence: first the atria contract and then the ventricles.

• Sinoatrial node (SA): cardiac pacemaker establishes normal heart rate, located in the posterior wall of the right atrium near the entrance of the superior vena cava.
• AV node: located in the wall of the right atrium, near the entrance of the coronary sinus.

These structures are made up of specialized heart fiber cells, the conduction cells. There are two populations of conducting cells:

• Nodal cells: responsible for heart rhythm.
• Conduction fibers: distribute the contractile stimulus to the muscle component.

Nodal cells are electrically connected to each other, to the conduction fibers, and to the myocardial fiber cells. Their membranes spontaneously depolarize up to the threshold level, generating an action potential that propagates through the conduction system reaching the muscle tissue and causing its contraction.

Cardiac cycle

1. Excitation begins in the sinoatrial node in the wall of the right atrium.
2. Action potential is transmitted through the atrial muscle fibers to the atrioventricular (AV) node.
3. From the AV node, the action potential passes into the atrioventricular (AV) bundle.
4. It is transmitted to the right and left branches of the bundle that run towards the apex of the heart.
5. The Purkinje fibers conduct the action potential first to the apex and then to the rest of the ventricular myocardium.

A cardiac cycle corresponds to the period of time between the start of one heartbeat and the start of the next and lasts about 0.8 seconds. The cardiac cycle includes alternating periods of systole (contraction phase during which blood is pushed into the adjacent chamber or arterial trunk) and diastole (relaxation phase during which the chamber fills with blood).

Heart rate

The heart beats 70/80 times per minute. Tissues require an inflow of different blood volumes according to different conditions. The most important factors in regulating the heart rate are the autonomic nervous system and hormones such as adrenaline and noradrenaline released by the adrenal glands.

Autonomic control of HR

Heart rate can be changed by:

• Acetylcholine released by parasympathetic neurons slows down spontaneous depolarization and therefore heart rate.
• Norepinephrine released by sympathetic neurons increases the depolarization index and heart rate.

In normal conditions of rest, the heart rate is around 80 beats per minute. An altered function of the pacemaker cells can cause bradycardia (heart rate lower than normal rate) or tachycardia (higher than normal rate).

Electrocardiogram

Electrical events (NO contraction) associated with cardiac depolarizations and repolarizations can be detected by electrodes placed on the ECG body surface. It is possible to obtain information about the function of the nodes, the conduction and contraction components, and identify anomalies in electrical conduction, such as arrhythmias.

ECG standard

• P wave: impulse propagates to the atria (atria depolarization).
• QRS complex: impulse propagates to the ventricles (ventricular depolarization and atrial repolarization).
• T wave: the ventricle relaxes (ventricular repolarization).

1. Atria begin depolarizing.
2. Atrial depolarization complete (P wave).
3. Ventricular depolarization begins at the apex and progresses superiorly as atria repolarize (QR).
4. Ventricular depolarization complete (QRS complex).
5. Ventricular repolarization begins at the apex and progresses superiorly.
6. Ventricular repolarization complete, heart is ready for the next cycle (T wave).

Anatomy (04/11/2022)

Respiratory system

• Gas exchange between blood and air.
• Air transport to the exchange surfaces.
• Smell.
• Phonation.
• Regulation of blood volume, pressure, and pH.

Why do we need O₂?

To produce ATP: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + 38 ATP.

Why this affects the blood pH:

CO₂ + H₂O → H₂CO₃ → HCO₃^- + H⁺

Components

• Lungs and respiratory tracts.
• Conducting portion: from nose to bronchioles (air is transported).
• Respiratory portion: from bronchioles to the alveoli (gas exchange).
• Upper respiratory system: filtering, warming, humidifying (nasal cavity, pharynx, larynx).
• Lower respiratory system (trachea, bronchi, lungs).

Respiratory epithelium

Pseudostratified ciliated columnar epithelium with numerous mucous cells.

• Cilia: sweep mucus toward the pharynx.
• Mucous lift: mechanism of defense.

The mucus is important to trap pathogens, and cilia are used to get rid of those pathogens by pushing the mucus towards the pharynx. Cilia are very vulnerable to toxic insults such as smoke, car exhaust, and infections.

Cystic fibrosis

Most common fatal inherited disease.

• Anomaly in the Cl channel which makes the mucus (+ respiratory tract) so thick that it cannot be moved by the cilia.
• All mucosal surfaces of the human body are affected; however, one of the most damaged organs is the airway: a layer of thick and sticky mucus plugs the airway ducts, resulting in respiratory difficulties and pulmonary failure.
• Reduction of the diameter of the respiratory tract and severe lung infections lead to death at a young age.

Nose and nasal cavity

The skeleton of the nose is composed of an upper bony portion and a lower cartilaginous portion. Proximal portions of the nostrils (alae) are composed of connective tissue with small embedded pieces of cartilage.

• The nose has two parts: external part (visible, consists of bone and cartilage with two openings called nostrils) and internal part (inserted inside the skull with posterior openings called choanae).
• From the nostrils to the vestibule, there are whiskers, sturdy hairs that trap large particles.
• The space inside the nose (nasal cavity) is located above the oral cavity.
• Nasal conchae (3): Superior, middle, and inferior promote filtration, heating, and humidification of incoming air.
• The paranasal sinuses (frontal, ethmoid, maxillary, and sphenoid) are air-filled cavities that reduce the weight of the skull: mucous secretion of the paranasal sinuses and tears keep the nasal passages moist and clean.
• The nasal septum divides the nasal cavity into two portions: nasal septum (hyaline cartilage + perpendicular plate ethmoidal bone + vomer).
• Deviated septum: normal position of the nasal septum creates two roughly symmetrical nasal cavities; extreme lateral deviation of the septum may result in the obstruction of the nasal passages.

Internal functions

• Humidification, heating, and filtration of inspired air.
• Detection of olfactory stimuli (smell).

Olfactory mucosa

Olfactory epithelium covers the roof of the nasal cavities (ethmoid lamina cribrosa, nasal septum).