To an Israelite under the Law of Moses, kidneys always made them think of sacrifice. The kidneys and the fat of all animal sacrifices had to be burnt upon the altar. “Then he shall offer from the sacrifice of the peace offering, as an offering made by fire to the Lord, its fat and the whole fat tail … all the fat that is on the entrails, the two kidneys and the fat that is on them by the flanks, and the fatty lobe attached to the liver above the kidneys … and the priest shall burn them on the altar as food, an offering made by fire to the Lord” (Lev 3:9–11 nkjv)
Figure . 1 :Iamp’s Kidney’s
The kidneys were offered in the peace offering, the sin offering and the trespass offering (Lev 3:4,10; 4:9; 7:4). Kidneys also featured in sacrifices for the priests’ sanctification (Exod 29:13,22; Lev 8:16,25; 9:10,19).
Why would the Father especially mark out the kidneys to be offered for so many sacrifices? Why not the heart or the lungs? The kidneys represent “the deep seated thoughts of one’s inner self. In these references where it is so used in Scripture, it is translated reins (Psa 16:7)” (Martin, 2005, p.17). The word translated reins and kidney in the av is the same Hebrew word, kilyah. The kidneys represent one’s deepest, innermost feelings. When our innermost thoughts are exercised and directed by the Word of God, they are of great value to Him.
“Behold, You desire truth in the inward parts, And in the hidden part You will make me to know wisdom” (Psa 51:6 nkjv). Also “he is a Jew who is one inwardly; and circumcision is that of the heart, in the Spirit not in the letter; whose praise is not from men but from God” (Rom 2:29 nkjv).
The spiritual significance and symbology of the kidney is explained in Psalm 26. “The Hebrew word for reins literally means kidneys. General scriptural usage indicates that it relates to the innermost motivation of a man. Whereas the heart (Heb leb) relates to the manifestation of a person’s emotions, thoughts and inclinations, the ‘reins’ are that part of a man which decides whether those thoughts and inclinations will be for good or evil. So the reins can be tried (Psa 7:9), can instruct (Psa 16:7) and can act as a person’s conscience (‘I was pricked in my reins’, Psa 73:21)” (Mellows, 1992, pp.318–319).
The kidneys are the most efficient filters in existence. As the kidneys filter out that which is bad and keep that which is good, so a man’s conscience will cause him to choose the good and reject that which is bad. This is exemplified in the Lord Jesus Christ of whom it was prophesied, “Therefore the Lord Himself will give you a sign: Behold, the virgin shall conceive and bear a Son, and shall call his name Immanuel. Curds and honey he shall eat, that he may know to refuse the evil and choose the good” (Isa 7:14–15 nkjv).
The kidneys “refuse” or excrete wastes and toxins while “choosing” to retain useful substances in the blood.
On a number of occasions we read that the Father tries both our reins and heart. “I the Lord search the heart, I try the reins, even to give every man according to his ways, and according to the fruit of his doings” (Jer 17:10 kjv).
To please Him, He wants more than just our emotions or heart. He also wants our inner deep thoughts and our conscience which directs and motivates us. “Now the purpose of the commandment is love from a pure heart, from a good conscience, and from sincere faith” (1 Tim 1:5 nkjv).
Our kidneys, however, are more than filters of our blood. The kidneys do not operate in isolation; they are wonderful organs that interact with many parts of the body.
The pituitary gland
At the base of the brain lies the body’s master gland of the endocrine system – the pituitary. This small gland (about 1 cm in diameter) secretes a number of hormones that affect how our body operates. It is unique in that it is the only endocrine gland that is directly connected to the brain via the hypothalamus. The pituitary is divided into three lobes, the anterior, intermediate and posterior. Each lobe secretes a different set of hormones. Of particular interest is the hormone released by the posterior lobe called arginine vasopressin or antidiuretic hormone (ADH). ADH regulates the absorption of water by the kidneys.
Figure 2: Relationship of kidneys to the “head”
(Images from Astrid Vincent Dinesen)
This is a case of the natural mirroring the spiritual. Our spiritual head is Christ. “And he put all things under his feet, and gave him to be head over all things to the ecclesia, which is his body, the fullness of him who fills all in all” (Eph 1:22–23 nkjv). “And he is the head of the body, the ecclesia, who is the beginning, the firstborn from the dead, that in all things he may have the pre-eminence” (Col 1:18 nkjv). Our inner man should be directed by our head, the Lord Jesus Christ.
Water regulation is essential for life. If the kidneys fail in this role, then without medical intervention we die. To control and retain water our kidneys must respond to the hormonal messages from the head. Water symbolises the Word (Eph 5:26), so for us to live spiritually we must retain this “water of life” (Rev 21:6).
But some have a seared conscience (1 Tim 4:2) and cannot retain water and are described as “wells without water” (2 Pet 2:17), “waterless clouds” and “twice dead” (Jude 12).
Diabetes
Most of us are aware of the modern diabetes epidemic. The most common form is diabetes mellitus where the body either does not produce enough insulin or does not respond to it. There is another form called diabetes insipidus. This disorder causes a person to produce tremendous quantities of urine. Up to 10 litres or more of urine a day is typical because the kidneys no longer respond to ADH. Too little ADH is produced or the kidneys fail to respond to it.
This is like those who love the water of the Word, but are unable to retain it. They fail to respond to their head through a faulty understanding of God, like those whom Paul describes in 2 Timothy 3:7 (nkjv) as “always learning and never able to come to the knowledge of the truth.”
Macroscopic structure of the kidney
Each kidney is bean shaped and roughly the size of one’s fist. Obtain and cut open a kidney; you will see that it is not uniform in structure. Look carefully and you will notice that there is some organization. There are three main areas. The outer more lightly coloured area is called the cortex; the middle, darker reddish-brown area, the medulla; and the central whitish, yellow funnel like area, the renal pelvis. These areas are more clearly shown by the artist in the following illustration.
Figure 3: Parts of the kidney
The blood supply
Both kidneys are only about 0.5% of total body weight. While quite small they receive a huge amount of blood, 20% of that pumped by the heart. This blood is filtered by the kidneys at a rate of about 125mL/minute. Over a 24 hour day this amounts to a staggering 180 litres. As the volume of blood in one’s body is 7–8 litres, the entire blood supply is filtered 20 to 30 times every day.
The nephron
Figure 4: A nephron (not of scale)
The kidneys are mentioned once in the New Testament. “And I will kill her children with death; and all the ecclesias shall know that I am he which searcheth the reins and hearts: and I will give unto every one of you according to your works” (Rev 2:23 kjv).
The Greek word for reins (kidney) is nephros. From this word we get nephrosis, the term for kidney disease, and nephron, the functional unit of the kidney. Every kidney has one to two million nephrons. A simplified nephron is depicted in Figure 4.
Every nephron starts with a structure called the glomerulus.
The spherical structure is called Bowman’s capsule and it houses a network of capillaries (the smallest blood vessels) known as the glomerulus capillaries. Combined these are called the renal corpuscle. The glomerulus is situated in the kidney’s cortex.
Blood enters the glomerulus through an arteriole, and blood pressure in the glomerulus forces water and dissolved substances and small protein molecules from the blood into Bowman’s capsule. This is called ‘filtrate’ and the kidneys generate about 40 litres of filtrate a day.
The glomerular filtrate flows along the first part of the renal tubule called the proximal convoluted tubule, then into the loop of Henle and finally along the distal convoluted tubule. The tubule wall is incredibly thin – just one cell thick – and has a large number of transport proteins within this wall. These transport proteins latch on to various small molecules in the filtrate as it flows past and moves them into the cell. Each transport protein is specific to one or two molecules. Sometimes useful molecules are passively transported back into the blood while others require energy. The kidneys are the second most active body tissue after exercising muscles. These amazing tiny tubules work very hard to maintain your blood chemistry!
Kidney tubule
In this first section of the nephron – the twisted proximal convoluted tubule – water, glucose, vitamins, amino acids, and minerals (sodium, potassium bicarbonate and chloride) are reabsorbed from the filtrate into the blood.
Next, the loop of Henle, is a narrow section of the nephron tubule that has a descending limb, a tight hair-pin bend and an ascending limb. From the diagram of the nephron one might think this loop is quite short. However the diagram is not to scale – it would be impossible to draw a scale diagram and still see the various structures. The loop is 2–3cm long, descending all the way from the kidney cortex down into the medulla and back to the cortex.
The reabsorption of water from the collecting tubules is controlled by the pituitary gland through the production of ADH. The absorption of water from the collecting tubules only occurs when ADH is present. The more ADH present the more water is absorbed.
The posterior lobe of the pituitary has special nerve cells that sense the concentration of salts in the blood. If the concentration is high, ADH is secreted and more water is absorbed. If the concentration is low, less ADH is excreted and less water is absorbed. The concentration of salts is directly related to the amount of water in the blood. The saltier the blood, the more water is reabsorbed by the kidneys and the more concentrated one’s urine becomes. As we drink more, the reverse happens and the volume of urine increases as the excess water is excreted.
The kidneys are very small organs but they are essential for survival and a healthy life. They work long and hard excreting toxic wastes and maintaining a constant internal environment by keeping the blood’s concentration within strict limits.
Kidney hormones and enzymes
The kidneys work in harmony with many other parts of the body to regulate:
- blood pressure via the production of the enzyme Renin
- calcium levels through the conversion of cholecalciferol into Vitamin D, and
- the manufacture of red blood cells by the secretion of erythropoietin (which is used by elite athletes to increase their red cell count).
The best medical technology cannot replicate all these functions of the kidney, like controlling blood pressure and the kidney’s rapid response to changes in our blood chemistry. People with kidney failure are helped by renal dialysis but the only cure for kidney failure is a kidney transplant. Only the organ Yahweh designed can do the whole job. We truly are wonderfully made. How could such an intricate organ with all its highly specialised anatomy and functions have come about by chance! How are the “wise (taken) in their own craftiness” (1 Cor 3:19).
In 1 Corinthians 12:20–31, Paul deals with the body and demonstrates that all our parts are important. No organ can operate independently of others and even those we rarely consider (“less honourable”) are vitally important. The kidneys fit this category; you don’t think about them until something goes wrong! They extract and excrete daily body wastes because these wastes are like “the sin which doth so easily beset us”. Wastes are the product of things we do. These intricate little organs that work constantly to keep us clean within are like the Word of God and the forgiveness that makes us spiritually clean. Kidneys are essential to the health of the whole body and they work in concert with other bodily organs.
Paul adds in verse 26, “And if one member suffers, all the members suffer with it; or if one member is honoured, all the members rejoice with it”(nkjv). So, if our kidneys suffer and fail, all the other members of the body are affected, even to the point of death. We are all members of the one body of Christ. “Now you are the body of Christ, and members individually” (1 Cor 12:27 nkjv). We must all be considerate of one another and not fall into the mistake of presuming some to be less or more worthy than others.
Martin, J. (2005). The Schoolmaster. CSSS.
Mellows, R. (1992). Psalms, An Introduction to the Psalter (1–41). CSSS.