Human Health Notes
Levels of Organization
Cells are the smallest independent living things in the human body. The body contains many different cell types, each with a specific function.
Cells are organized into tissues. A tissue is a group of similar cells working together to perform a specific function.
An organ is an identifiable body structure composed of two or more tissue types.
Organs often perform specific physiological functions, such as the stomach aiding in food digestion.
An organ system is a group of organs that work together to perform a specific function. For example, the digestive system includes the stomach, small intestine, and large intestine, which work together to digest food, move nutrients into the blood, and eliminate waste.
The human organism, the most complex level of organization, is composed of many organ systems that work together to perform the functions of an independent individual.
Circulatory System
Living cells require water, nutrients such as glucose (sugar) and amino acids (proteins), and oxygen. They also need waste products from cellular respiration removed.
The more active an organism, the more nutrients its cells require, increasing the need for an efficient internal transport system.
Larger animals have a blood circulatory system that connects body parts and provides resources where needed.
The human body has a closed circulation where blood is pumped by a muscular heart and circulates in a continuous system of tubes: arteries, veins, and capillaries under pressure.
Heart Structure
The human heart is a hollow, muscular organ about the size of a clenched fist, located between the lungs. Heart muscle fibers contract rhythmically from formation until death. Muscles typically contract when stimulated by a nerve supply.
The heart's cavity is divided into four chambers: the right and left sides are completely separate.
The two upper chambers are thin-walled atria (singular: atrium), which receive blood into the heart.
The two lower chambers are thick-walled ventricles. The muscular wall of the left ventricle is much thicker than that of the right ventricle, as the ventricles pump blood out of the heart.
Blood Pathway
The cardiac cycle is the sequence of events of a heartbeat, which pumps blood throughout the body.
Starting with Pulmonary circulation:
Contraction of the right atrium pushes blood past the atrioventricular valve into the right ventricle, where the pressure is low because the atrium's wall is thin and cannot create much pressure.
The atrium relaxes.
Next, the right ventricle contracts, forcing blood into the lungs.
The right side of the heart pumps deoxygenated blood to the lungs through the pulmonary artery.
In the lungs, carbon dioxide diffuses from the blood, and oxygen is absorbed into the blood.
The oxygenated blood flows to the left atrium of the heart through pulmonary veins.
Systemic Circulation:
The left side of the heart pumps oxygenated blood to the rest of the body.
In systemic circulation, organs are supplied with blood by many arteries branching from the aorta.
The left atrium contracts, pushing blood to the left ventricle, which contracts, forcing oxygenated blood to all body cells.
Cells absorb needed oxygen and load the blood with carbon dioxide, and the blood returns to the heart from the superior and inferior vena cava.
Valves
The valves of the heart prevent the backflow of blood, which helps maintain the direction of flow through the heart.
Atrioventricular valves are large valves that prevent backflow from ventricles to atria. The tricuspid valve is on the right side, and the bicuspid (or mitral) valve is on the left.
Semilunar valves separate the ventricles from the pulmonary artery (right side) and aorta (left side). These prevent backflow from the aorta and pulmonary artery into the ventricles as the ventricles relax between heartbeats.
Blood Vessels
Arteries
Arteries are blood vessels that carry blood away from the heart.
Arteries have a relatively thick muscle layer that contracts and relaxes under nerve control, allowing them to pulsate.
In addition to muscles, arteries have elastic fibers that help maintain the high blood pressure achieved by ventricular contractions.
Blood in arteries is at high pressure because arteries are directly connected to the ventricles of the heart.
The peak pressure in an artery is called systolic pressure, which widens the lumen (internal part) and stretches elastic fibers in the wall.
All arteries carry oxygenated blood, except the pulmonary artery.
Blood Capillaries
These are tiny microscopic vessels that connect artery branches (arterioles) with vein branches (venules).
They spread in the spaces between body cells to reach all cells and supply them with food and oxygen.
Their walls are very thin with tiny pores, facilitating the quick exchange of substances between blood and cells.
Chemical exchanges always occur through the capillaries because the walls of arteries and veins are too thick.
Veins
Veins receive blood at a relatively low pressure from the capillaries and return it to the atria of the heart.
All veins carry deoxygenated blood, except pulmonary veins.
Blood flow through veins is slower than through arteries due to the loss of blood pressure.
Veins do not need as thick walls as arteries and contain far fewer muscle and elastic fibers.
Veins have many internal one-way valves that help keep the slow-moving blood traveling consistently towards the heart.
Blood Components
Blood is the medium by which digestion products are transported and plays key roles in the body’s defense against disease and in respiratory gas transport.
Blood is composed of a liquid medium called plasma in which cells are suspended: red blood cells, white blood cells, and platelets.
Plasma
Plasma is composed of:
90% Water
7% soluble proteins
1% Salts (fibrinogen)
2% other components (Hormones, chemicals, Glucose, wastes and antibodies)
Plasma functions:
Transporting wastes (urea) to the kidney for removal in urine.
Transporting hormones (chemical messengers) from glands to tissues and organs.
Transporting antibodies for immunity, destroying germs and bacteria.
Transporting nutrients from the digestive system to all cells.
Red Blood Cells (Erythrocytes)
Red blood cells carry oxygen throughout the body.
They are biconcave in shape, thin in the middle.
This shape makes them flexible, so they move easily through blood vessels and exchange oxygen with their surroundings more quickly.
Red blood cells get their bright red color from hemoglobin, a protein that carries oxygen from the lungs to other tissues.
Red blood cells lack a nucleus, allowing them to move throughout your body easier.
Hemoglobin has binding sites for oxygen, greatly increasing the blood's capacity for oxygen transport. Oxyhemoglobin is bright red, while carbaminohemoglobin () is dark red.
After circulating for about 120 days, they are removed and regenerated from the bone marrow.
White Blood Cells (Leukocytes)
White blood cells are part of your immune system, protecting your body from infection.
They circulate through bloodstream and tissues to respond to injury or illness, attacking unknown organisms.
White blood cell formation occurs inside your bones (bone marrow).
These cells are colorless.
They are round shaped with a distinct center nucleus that differs based on their function and type.
Checking the number of WBC in the blood is usually part of a complete blood count (CBC) test to look for conditions such as infection, inflammation, allergies, and leukemia
The lifespan of white blood cells (WBCs) varies widely from hours to decades, depending on the WBC type and whether they are activated or in a resting state.
Platelets
Platelets are enucleate (lack a nucleus) and survive in the bloodstream for about 7–10 days.
Platelets form in the bone marrow.
They play a role in blood clotting.
Mechanism of Blood Clotting
When a small blood vessel is damaged:
Damaged cells release chemicals that stimulate platelets to adhere to the damaged area.
The damaged tissue and platelets release chemicals called clotting factors that convert the soluble fibrinogen into the insoluble fibrin
Fibrin is a protein that forms a mesh-like network that helps to stabilize the platelet plug.
More and more cellular debris becomes trapped in the fibrin mesh, and soon a stable clot has formed, preventing both further blood loss and the entry of pathogens.
Coronary Arteries and Coronary Heart Diseases
Each individual has small holes visible on the inner surface of the aorta, near the semilunar valve, which is the opening to the coronary arteries.
The coronary arteries supply the cardiac muscles (heart muscles) with oxygen and nutrients, which are essential for the pumping action.
They also remove the waste products.
Coronary Heart Diseases
Heart muscle works throughout our lives and requires constant supplies of blood.
Three large coronary arteries branch from the aorta and supply heart muscle with oxygen-rich blood.
If any of the three arteries is blocked, an area of the heart will receive less oxygen, which may stop contracting or die.
A blockage in a coronary artery or one of its branches is known as a coronary thrombosis or heart attack.
The cause of coronary heart disease (CHD) is often damage to the arteries.
One serious cause of damage is atherosclerosis, a slow degeneration of the arteries caused by a build-up of plaque inside them.
Plaque becomes attached to lining of an artery and can accumulate over many years.
Few people suffer from any symptoms before middle age.
The lining may become damaged and thickened because lipids and cholesterol accumulate.
Over time, the diameter of the artery becomes restricted so that blood cannot flow along it properly.
As the rate of flow slows down, blood may clot in the artery, further restricting the movement of blood along it.
Clots may also break free and travel to block another smaller artery elsewhere in the body. If this artery is in the brain, the clot may cause a stroke.
Respiratory System
All living cells need energy for their activities.
Energy is released from the breakdown of glucose and other substances during the process of cell respiration.
Respiration is a chemical reaction that occurs in mitochondria and the cytoplasm and releases energy.
Our cells use oxygen to carry out aerobic respiration and produce carbon dioxide as a waste product.
Oxygen is taken in from the air and carbon dioxide is returned to it in a passive process known as gas exchange.
Gas exchange occurs in the alveoli of the lungs where oxygen from the air diffuses into blood capillaries, and carbon dioxide passes in the opposite direction.
Air Pathway
Air enters the respiratory system, it is warmed and filtered in the inner nasal cavity
Air then moves from the nose to a cavity at the back of the mouth called the pharynx, or throat, and then into the trachea, or windpipe passing through the larynx (voice box) which contains two highly elastic folds of tissue known as the vocal cords.
Entry into the larynx is via a slit-like opening, the glottis. Above is a cartilaginous flap, the epiglottis. Glottis and epiglottis work to prevent the entry of food into the trachea.
Incomplete rings of cartilage in the trachea wall prevent collapse under pressure from a large bolus of food passing down the esophagus.
Mucus produced in the trachea traps inhaled particles, which cilia then sweep away from the lungs toward the pharynx.
From the trachea, air moves into two large tubes called bronchi leading to the lungs.
These tubes divide into smaller bronchi, and then into even smaller bronchioles
Bronchi and bronchioles are surrounded by smooth muscles that regulate the size of air passageways.
The bronchioles lead to several hundred million tiny air sacs called alveoli, A delicate network of capillaries surrounds each alveolus.
Inhalation and Exhalation
Lungs have no muscles and cannot move by themselves.
Breathing is brought about by two sets of muscles between the ribs, and by the diaphragm, the sheet of muscle separating the thorax from the abdomen
During inhalation, contraction of the external muscles and contraction of the diaphragm raises the ribs. These movements increase the volume of the chest cavity.
As a result, air is drawn down the trachea to fill the lungs.
Gentle exhalation occurs as the muscles and the diaphragm relax, reducing the volume of the chest cavity.
Structure of Alveoli and Gas Exchange
A capillary system wraps around the clusters of alveoli.
There are some 700 million alveoli in our lungs, providing a large surface area
The wall of an alveolus is very thin, it’s composed of single layer of cells
The capillaries that wrap around them also have thin walls of single epithelial cells.
These two thin layers make the distance for diffusion of gases as small as possible. Oxygen diffuses through the alveolus and capillary into the blood and carbon dioxide diffuses in the opposite direction.
So long as the diffusion gradient is maintained by regular breathing, diffusion continues.
Diffusion
Diffusion is the free passage of molecules (and atoms and ions) from a region of their high concentration to a region of low concentration.
It’s influenced by several factors such as:
Surface area: A larger surface area increases the rate of diffusion, the alveoli provides a vast surface area for gas exchange
the concentration gradient: The greater the difference in gas concentration between 2 sides of the membrane, the faster the diffusion rate.
Thickness of the exchange surface: A thinner membrane allows faster diffusion, the alveolar-capillary barrier is very thin, facilitating efficient gas exchange
Size of particles: the smaller molecules such as (oxygen and ) can pass freely
Digestive System
When you eat a snack or meal, a series of events is begun that leads to your body cells being provided with the nutrients that they need. The order of events is:
Ingestion – you eat the food
Digestion – a series of chemical reactions occurs, whereby the ingested food is converted into smaller and smaller molecular forms.
Absorption – small molecular forms are absorbed through the cells of your digestive system and pass into nearby blood or lymphatic vessels
Transport – your circulatory system delivers the small molecular nutrients to your body cells.
assimilation: products of digestion are absorbed from blood into body cells (such as liver and muscle cells) and used or stored
Egestion: undigested food and dead cells from the lining of the gut, together with bacteria from the gut flora, are expelled from the body as faeces
Process | Definition |
|---|---|
Ingestion | taking food into mouth |
Digestion | breaking down food into soluble molecules |
Absorption | taking products of digestion into bloodstream |
Assimilation | using products of digestion for e.g. respiration, making proteins |
Egestion | removal of undigested food |
Digestion is the mechanical and chemical breakdown of food into smaller, more soluble components.
Digestion
An animal takes in food, which is complex organic matter, and digests it in the alimentary canal or gut, producing molecules that can be taken up into the body cells via the blood circulation system
The mammalian gut is a long, hollow muscular tube connecting mouth to anus.
The bulk of the food which is taken into the gut consists of insoluble molecules that are too large to cross the gut wall and enter the bloodstream. Our diet largely consists of carbohydrates, lipids and proteins. These must be hydrolyzed (broken down by hydrolysis) to simple sugar, fatty acids and glycerol, and free amino acids before they can be absorbed and, later, built up into the carbohydrates, lipids and proteins required by our bodies
Types of Digestion
The first stage in the breakdown of large, insoluble food molecules is mechanical digestion.
This occurs by the action of the jaws and teeth in the mouth, and, later, through the churning action of the muscular walls as the food is moved along the gut, particularly in the stomach.
Throughout the gut, waves of contraction and relaxation of the circular and longitudinal muscles of the wall propel food along. This process is known as peristalsis
As food moves through your alimentary canal, many digestive enzymes are added to it along the way.
Each digestive enzyme is special for a special food type
As you may know, enzymes are protein molecules that act as catalysts for reactions. As catalysts, the function of enzymes is to speed up chemical reactions without being affected
Digestion is completed by the enzymes that were secreted onto the food (chemical digestion)
Food is broken down by two actions:
PHYSICAL /MECHANICAL
CHEMICAL
Digestion Process
The human digestive system is a tube called the alimentary canal. In order, the alimentary canal consists of:
Mouth
esophagus
stomach
small intestine
large intestine (colon)
rectum
Digestion in Mouth
The first stage of the digestive process involves both mechanical and chemical digestion:
Mechanical digestion:
The teeth break down food into smaller pieces through “ chewing “
The tongue helps mix the food with saliva and forms it into a soft mass called “bolus”, making swallowing easier
Chemical digestion
The salivary glands produce saliva, which contains enzymes and mucus to softens the food and facilitate its swallowing
The enzyme salivary amylase (ptyalin) starts breaking down starch into simple sugar
After this, the bolus is pushed to the back of the mouth and swallowed, passing through the pharynx and esophagus
Esophagus
It follows the pharynx, where it passes through the neck and into the chest cavity
Its lining contains glands that secrete mucus, which helps lubricate the bolus and makes it easier to slide down
It has muscular walls that contract and relax in wave like motion called peristalsis
This pushes the food bolus downward toward the stomach, even if you’re lying down or upside down
At the end of the esophagus, the cardiac sphincter opens to allow food into the stomach and then closes to prevent stomach acid from flowing back
Digestion in Stomach
The stomach, a J-shaped muscular bag, is located high in the abdominal cavity, below the diaphragm and liver
Once in the stomach, the food is held for a period of time in order to mix it with a variety of secretions collectively known as gastric juice
It’s a mixture of three secretions from the cells of the stomach inner lining
Pepsin- a protease enzyme most active in acidic pH – helps in breaking down proteins
Hydrochloric acid “HCL”- activates pepsin enzyme, creates acidic environment, kills many of the bacteria present in the incoming food
mucus- lines the inside of the stomach wall to prevent stomach damage from the hydrochloric acid
The food is now mixed with gastric juice and churned by muscle action, becoming a semi- liquid called chyme. This churning action is an important part of the mechanical digestion process.
After a period of time, the pyloric sphincter opens and the food enters the small intestine
Small Intestine
It follows the stomach, It’s about 5, 5.5 meters long
Final stages of digestion of lipids, carbohydrates, and proteins, neutralizing stomach acid, plus absorption of nutrients
Food enters the first part of the small intestine a little at a time. Here the chyme meets bile from the liver and the pancreatic juice from the pancreas.
Bile is strongly alkaline and neutralizes the acidity of the chyme. It’s secreted from the liver but the gall bladder stores and controls its release
It also breaks down the large fats into tiny droplets, This speeds digestion by the enzyme lipase, later on. Bile itself contains no enzymes.
Pancreatic juice contains several enzymes, including:
Pancreatic amylase that catalyzes the hydrolysis of starch to a simple sugar
Lipase that catalyzes the hydrolysis of fats to fatty acids and glycerol
Proteases – helps in breaking down proteins into free amino acids
Absorption
The cells in the inner lining of the small intestine has many small folds or projections called villi (singular villus)
The epithelial cells have tiny membrane projections called microvilli that extend into the lumen of the intestine.
The villi and microvilli greatly increase the surface area for absorption within the small intestine, compared with a smooth-walled structure.
The interior of each villus contains a capillary bed for nutrient absorption and transport of digested food to the bloodstream by diffusion. In addition, there is a small vessel present, called a lacteal, that absorbs some of the nutrients (fatty acids)
* The larger the surface area, the faster molecules can move into (or out from) an organism.
For example, the folds in the lining of the small intestine (the villi) allow digested food molecules to move into the blood at a rate that is fast enough to maintain life processes. Further folds on the membranes of the cells lining the intestine (microvilli) further increase the surface area.
Here is a partial list of the substances absorbed through villi into the bloodstream or lacteal vessel:
water
glucose (plus other simple sugar)
amino acids
fatty acids
mineral ions
vitamins
Large Intestine
The large intestine wall has no villi, but the surface area for absorption is increased by many folds of the inner lining.
At this point in the gut, most of the useful products of digestion have been absorbed. What remains is the undigested matter (such as plant fiber), with mucus, dead cells, bacteria, some mineral ions and water.
Water is an important component of our diet, and many liters of water are also secreted into the chyme in the form of digestive juices.
In the colon, water and mineral salts (such as and ions) are absorbed.
What remains of the meal is now the faeces. Bacteria compose about 50% of faeces.
The rectum is a short muscular tube which terminates at the anus. Discharge of faeces from the body at the anus happens by the contraction of the rectum and relaxation of controlled sphincter muscles
Types of Nutrients
Macro-nutrients | Micro-nutrients |
|---|---|
Nutrients needed by the body in large amounts Carbohydrates, Proteins, Fats, fibers They are essential for our survival as they provide energy and support body structure Rice (carbs) Meat (protein) Oil (fat) | Nutrients needed by the body in small quantities Vitamins (A, B, C, D, E, K), Minerals (Iron, Calcium, Iodine, etc.) They don’t provide energy Support the immunity, and development Oranges (Vitamin C) Milk (Calcium) |
Carbohydrates
When planning what to eat, in order to have the suggested balance of macronutrients, it is important to know that not all kinds of carbohydrates, fats, proteins and fiber are the same.
Our cells are able to process some sources of macronutrients better than others. In other words, some sources of macronutrients are of a higher quality than other sources.
For example, brown rice, an example of a complex carbohydrate, is a higher quality source of carbohydrates than candy, a simple sugar.
This is because it takes the body longer to break down the complex carbohydrates “starch” into glucose, which means the cells will be able to produce energy at a slower but more steady rate.
Contrast this to the energy that comes from eating candy or other sugary foods: simple sugars are quickly broken down into glucose, so the cells produce a large amount of energy quickly, leaving us feeling tired and un-energized afterwards.
Fats
There is also a difference in the quality of fats that we eat.
Some fats - like the oils from olives, avocados, nuts and salmon - are examples of unsaturated fats. These are often referred to as 'good fats' and are usually a liquid at room temperature. Doctors recommend that 90% or more of your daily intake of fats should come from unsaturated fats.
Saturated fats, on the other hand, are found in foods like butter, beef, the dark meat of chicken, bacon, and processed meats like salami. These fats are solid at room temperature. Saturated fats are often described as 'bad fats', and doctors recommend that they make up 10% or less of what you eat.
Another type of fat, called trans fat, is often used to fry fast foods like chips, and to make commercially processed foods like cookies, cakes, or microwaved popcorn. most are formed artificially through a chemical process that converts unsaturated liquid fats to saturated solid fats.
When added to foods, trans fats give baked goods a soft and appealing texture and provide a cheap alternative to frying oil that has a longer shelf life than natural frying oils, However, despite these appealing characteristics of trans fats, they are potentially harmful to your health, and doctors recommend that you avoid them completely.
Saturated and trans fats raise the level of another type of fat, called low-density lipoprotein cholesterol (or LDL cholesterol), in our blood causing blood vessel narrowing and blockages; leading to heart attacks or strokes.
Unsaturated fats, however, can raise the level of high-density lipoprotein cholesterol (or HDL cholesterol) in our blood. HDL cholesterol picks up and transports LDL, preventing the build up of the latter.
Proteins
There are many different proteins, each one defined by the combination of amino acids of which it is made. There are two main types of dietary proteins: plant-based and animal-based.
Animal proteins—found in meat, chicken, fish, eggs, and dairy—are considered 'complete' proteins because they contain all essential amino acids.
plant proteins—such as those found in beans, lentils, nuts, seeds, and grains—are typically 'incomplete,' meaning they lack one or more of the essential amino acids. By eating a variety of plant-based foods throughout the day it's possible to get all essential amino acids and meet protein needs effectively.